| Surveying | |
Use only horizontal ground distance [not grid distance] dimensions in land surveys
In Australia, all land dimensions are only horizontal ground distances and all surveying and mapping coordinates are only on 60 UTM projection. Comparatively simple and unconfused, this Australian coordination practice has proven itself over the last 50 years and can claim to be the best survey coordination and mapping system in the world |
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Abstract
The anomaly of having two nearly identical units of linear measurement has led the USA to discontinue the use of the “US Survey Foot” after 1/1/2023, This then leaves the “International” foot as the only standard unit of linear measurement in the USA. However, the USA also has two nearly identical ways of stating dimensions in land surveys. Either Grid distances on their SPCS coordinate projection plane [usually at Sea Level] or Horizontal Ground Distance [where measured and used] are stated as dimensions. The continuation of this anomaly and duplexity prompts this Paper.
Back in the 1970’s, in New South Wales, Australia, the reverse situation arose. Then, the surveying profession proposed a similar to SPCS coordination system that required Projection [Grid] distance [instead of the established horizontal ground distance that everyone was using] as dimensions on survey and title plans. Also, so that the proposed grid distance dimension approximated horizontal ground distance, they required a 20 zone UTM projection [in addition to the established 60 UTM mapping projection]. This Paper recounts the rationale used to ultimately reject the NSW proposal.
In Australia, all land dimensions are only horizontal ground distances and all surveying and mapping coordinates are only on 60 UTM projection. Comparatively simple and unconfused, this Australian coordination practice has proven itself over the last 50 years and can claim to be the best survey coordination and mapping system in the world.
1. Introduction
Upon the colonisation of New South Wales in 1788, all land was “taken” as Crown land [Public domain] and was leased or granted for settlement by metes-and-bounds visible marking and written description. Surveyors used circumferentors and compasses with reference to magnetic north for bearings and used a Gunther’s chain for measurement of boundaries. Later [1872] after the use of theodolites became mandatory and when a long, thin, steel riband or wire came into use, there was a significant improvement in the precision of surveys. Chains required regular standardisation to ensure accuracy. Together with the concise, simple and easily understood Torrens title system [introduced by the Real Property Act in 1863] real property was defined by precise boundaries physically identified on the ground and described in simple and easily understood terms. For nearly 100 years [in the 1970’s] this NSW survey and land title system underpinned property values and had proven itself to be reliable and trusted.
1.1 NSW trigonometrical surveys and mapping
Trig surveys and mapping in NSW had a haphazard past because of changing budgetary priorities. Consequently, Australia was caught unprepared during World War 2 and aerial surveying and mapping then became a military priority. In 1945 the National Mapping Council was established and resources optimised to meet Commonwealth, Military and State topographical mapping needs. Universal Transverse Mercator [UTM] projection was used with map sheets based on the International Map of the World [IMW] 60 longitude by 40 latitude sheets. The Australian Geodetic Datum [AGD] and the Australian Map Grid [AMG] were established in 1966 and were applicable in the 1970’s.
1.2 Coordinated cadastre
The NSW colonial cadastre was a patchwork of parcels where new parcels generally abutted existing parcels, using their abuttals for boundary origin and azimuth. Crown land portions and allotments were plotted on County, Parish, Town and Village maps and, after 1863, subdivision lots were plotted on Registrar General charting maps, together making up a mosaic of parcels for cadastral maps. The 1985 review of the state survey system established a Digital Cadastral Database [DCDB] which digitised data [1984- 1994] from AMG maps, aerial photos and calculated from surveys. This met most community need for coordinates without survey precision. It should be noted that the DCDB is graphical in nature, is used for administrative purposes, and has no legal weight in land boundary definition.
1.3 Boundaries and survey coordination
Boundary location is a matter of law whereby precedence is given to where boundaries are visible, identified or marked on the ground. The plan of survey records, in a convenient form, particulars of the survey of that boundary. In survey coordination, all other evidence of boundaries [visible, natural, marked, relocated from monuments, occupations and measurement] precede that of [invisible] coordinates. However, survey coordination provides point reference to underpin the coordinated cadastre and provides positional recovery where boundaries are destroyed by natural disasters such as bushfires and floods.
Survey coordination does not remove the obligation on the part of the surveyor to accurately mark boundaries on the ground as permanently and visibly as possible and to state the boundary information on the title plan that is clear and easily understood. For any legal credence in boundary definition, coordinates (and their datum) must be stated on the relevant survey or title plan.
1.4 The NSW survey integration proposal
The NSW Survey Integration proposal was timely. It was claimed to be “the first comprehensive system of surveys in the state”. It sought to replace [1] magnetic north, true north and azimuth from abuttals with grid north and [2] to integrate ad-hoc surveys with control surveys and a coordinated cadastre. It also [and this was a matter of subsequent dispute] proposed coordination copied from similar ‘narrow zone’ coordinate systems from overseas. It proposed that: [a] all stated land, survey and title dimensions be Projection [or Grid] distances on a coordinate projection plane [at sea level] and [b] proposed a ‘narrow’ 20 zone wide Integrated Survey Grid [ISG} so that [Grid distance] dimensions would be mathematically consistent with the proposed [ISG] coordinates. This was additional to the already existing horizontal ground distance dimensions and 60 Australian Map Grid [AMG].
The NSW proposal had support of the Surveyor General, academic surveyors, surveying professional bodies and the heads of most government Departments. This, and its use overseas, gave it credibility. Further, any argument against the matter under dispute was seen as opposition to the proposal as a whole, and was ignored by its NSW proponents.
Ultimately grid distance dimensions were opposed, and then [1975] rejected, so that all dimensions in surveys and land titles remained and continued as horizontal ground distances in Australia. Once this decision was made (and the need for grid distance dimensions on plans and their closeness to ground distances was no longer an issue), the existing 6° UTM (AMG) map projection should have also been used for survey coordination. Nevertheless, the 20 zone ISG was introduced and practised in NSW for 20 years (until 1995) when the geodetic 6°-zone AMG was replaced by the geocentric 6°- zone MGA. From then, and for the last 25 years, all survey and mapping coordinates, the DCDB and all maps have been based on the 6°-zone MGA (first MGA94 and now MGA2020).
This background information is included with the hope that the reader will forego the presupposition, generally accepted with the NSW proposal, that the grid distance dimension and ‘narrow zone’ coordination practised elsewhere around the world was the only means of survey-precision position reference. This paper argues against the statement of grid distances as dimensions in survey and land titles as they often differ with horizontal ground distance and other dimensions where measured and used. It also asserts that it is advantageous to state horizontal ground distance dimensions with an orientation to grid north and the already existing 6°-zone UTM mapping coordinate system, particularly in relation to modern surveying equipment producing more precise measurements and modern computer software simplifying and speeding up the calculation of coordinates. As horizontal ground distances and 6°-zone UTM maps already exist globally, this Australian system could be established worldwide, simply by doing away with the duplexity of grid distance dimensions and their ‘narrow zone’ coordination.
2. An initial explanation
In mapping, all distances on the projection plane are grid (or projection) distances, being in standard linear units on that plane. Distance on the ground, where measured and used, is in standard linear units at ground level. Consequently, grid distance dimensions (in ‘narrow zone’ coordination) vary from place to place and height to height with the distance measured at ground level by (1) a scale (projection) factor and (2) a height (above sea level) factor. These are combined as the ‘grid-to-ground’ conversion factor between grid and ground distances. As mathematical consistency of data is required in calculation, this must be in standard linear units, either on the projection plane or at ground level, with the ‘grid-to-ground’ conversion between them. (Mathematical consistency is when data or units of calculation are of the same uniform standard measure.) This conversion is ignored in many ‘narrow zone’ coordinate systems where grid distances are stated as ‘substantially equal’, ‘near enough’, ‘quasi-’ and/or ‘pseudo-’ horizontal ground distance dimensions.
In surveys, precision and accuracy of measurement is important and expected of a surveyor. The surveyor makes adjustment (not corrections, unless there is an error) to replicate the exactness of the standard linear units of their measurement. All measurements are adjusted to the horizontal or level at its mean height. This is known as “horizontal ground distance” (also called site or terrain distance) and is defined as “the distance on the horizontal plane at the mean elevation of its measurement”.
The matters of dispute between the NSW Survey Integration proposal and the alternative existing horizontal ground distance dimension –60
AMG coordinate proposal were:
[a] mathematical consistency and
[b] what to show on plans.
Copied from overseas practice [1] the NSW 2° ‘narrow zone’ coordination proposal required the mathematical consistency of data for calculating coordinates, thereby showing both projection [grid] dimensions and coordinates, on plans. This requires a ‘narrow zone’ projection to minimise the size of the ‘grid-toground’ conversion factor so when grid distance is stated as a dimension on plans, it approximates horizontal ground distance and measurement.
By comparison, [2] the existing alternative preserves the fundamental mathematical consistency of data between measurement and dimension. This means that horizontal ground distance dimensions and projection coordinates are shown on plans, but it requires the calculation of the ‘ground-to-grid’ difference between them for coordinate calculation. Unlike the NSW proposal with approximate dimensions, the existing alternative ensures the exactness of dimensions with measurement in standard linear units where measured and used.
So, the choice in the 1970s NSW Survey Integration debate was either:
1. introduce the overseas practice of mathematical consistency of the coordinate calculations derived from measurement, but stating grid dimensions on plans that [often] disagree with those measurements; or
2. maintain the long accepted mathematical consistency of horizontal ground distance dimensions with measurement and calculate the projection coordinates from measurement, but then, state on plans, dimensions that agree with those measurements.
3. Horizontal ground distance land dimensions, only and always
According to the Oxford Dictionary, a dimension is a measurable extent of any particular kind, such as length, breadth, depth or height. The word comes from the Latin dimensis meaning “a measuring” and the old French word dimetiri meaning to “measure out” and, hence, has a direct nexus with measurement. It is the written statement of a measurement.
Over many years the standardisation of units of measurement has been refined to the extent that standard linear units can be reproduced with exactitude. The dimension should replicate that exactitude as measured in standard units. Every country maintains national linear standards (in Australia, by the National Measurement Institute) and every surveyor must verify their measuring equipment with baselines certified from these standards. Consequently, every measurement (and dimensions derived from these measurements) should replicate the “most scrupulous exactness” of the standard linear unit.
Horizontal ground distance is the survey measurement and land dimension that a surveyor determines and what the public understands and expects. In this context, the deliberate departure [no matter how small] of grid distance from horizontal ground distance dimension at its location, would seem to be a specious practice by surveyors. Being ‘near enough’ is contrary to the professionalism expected of surveyors and the competence, precision and exactitude of the measurement surveyors make, and the dimensions that they then state.
3.1 Advantages of using Horizontal Ground Distance dimensions
Horizontal ground distance is stated in standard linear units, i.e. metres in Australia. Its use (instead of grid distance) is supported by the following five reasons outlined in the following subsections.
3.1.1 Measurement and usage support Horizontal Ground Distance dimensions
Usage (practically all development is built on the horizontal plane where their measurement is made), calculation, and convenience of record commonly support horizontal ground distance as the dimension in land measurement, surveys, property plans and titles.
3.1.2 Horizontal Ground Distance dimensions are mathematically consistent with all other dimensions in standard linear units
Horizontal ground distance maintains mathematical consistency with existing and other dimensions and their interrelated systems of area, volume, etc. In this context, this mathematical consistency is particularly important in design when construction materials and products are manufactured or prefabricated off-site. Incidentally, grid distance dimensions are the only exception to this mathematical consistency and the statement of dimensions in standard linear units where they are measured and used.
3.1.3 Horizontal Ground Distance Dimensions are mathematically consistent with measurement at specific locations, heights and surfaces
It would be illogical for metes and distance relative to bounds, distances to and from monuments, strata and strata titles, and titles restricted to often 50’ (15.24 m) from the surface, to be shown by standard linear unit dimensions at any other place (i.e. the projection plane or at sea level) than the location, height and surface to which such distances and areas are referred to, measured and used.
3.1.4 Horizontal Ground Distance dimensions do not change with Coordinate Systems
Unlike grid distance, horizontal ground distance does not change, irrespective of the zone width and coordinate system used. (Grid distance dimensions can vary, and be an issue, when more than one zone width or coordinate system is used, as in the 2°-versus-6° zone debate regarding the NSW proposal.)
3.1.5 ‘Narrow Zone’ Projection Coordinate Systems, State Plane Coordinate Systems and Low Distortion Projection Coordination acknowledge the significance of Horizontal Ground Distance
Specifically, the important function of horizontal ground distance is acknowledged by those systems designed to limit the difference between their grid (or projection) distances and the horizontal ground distance. However, the fundamental consideration is not an ‘acceptable’ amount of difference, but the need to have a difference, any difference, between the [grid distance] dimension shown and the horizontal ground distance measurement of what exists.
The statement of horizontal ground distance allows dimensions to be readily measured and used [1] without any need for ‘grid-to-ground’ calculation, [2] without the imprecision of (often) approximate grid distance dimensions, [3] without coordination, and [4] without a ‘narrow zone’ projection. This is what most users [and surveyors] want.
4. Grid distance land dimensions, not now and not ever
4.1 Use and Statement of Grid Distance dimensions on ‘Narrow Zone’ Projection Planes
Initially, in plane coordination, dimension and measurement were the same, and there was mathematical consistency with plane coordinates. Naturally, this mathematically consistent relationship could not be maintained over larger land areas and greater height differences, so measured (horizontal ground distance) data had to be multiplied by a ‘ground-to-grid’ conversion factor for coordinate calculation on the projection plane (Figure 1).
The introduction of mapping coordinates using UTM maps and survey coordinates using State Plane Coordinate Systems [SPCS] in the 1930s was revolutionary at the time and continued to underpin the ‘narrow zone’ NSW Survey Integration proposal of the 1970s. The validity of calculation requires mathematical consistency of all data used in the calculation. This is irrefutable and forms the basis of support for the mathematical consistency of grid distance dimensions and coordinates.
However, this created a paradox where the precision of the ‘ground to grid’ conversion applied when initially establishing coordinates from measurement, did not apply in reverse when the comparatively imprecise grid distance dimensions used in ‘narrow zone’ coordination was stated on plans. That is, without the ‘grid-to ground’ conversion, the stated grid dimension was imprecise and mathematically inconsistent with the measurement from which it was derived. Also, grid distance dimensions required ‘grid-to-ground’ calculation every time for the more precise Horizontal ground distance dimension was needed, even if coordination was not used.
Essentially, the real issue was whether, or not, grid distance should be shown as dimensions on plans. The NSW ‘narrow zone’ coordinate supporters argued that it should, otherwise the mathematically inconsistent data would invalidate coordinate calculations. So, instead of mathematical consistency of stated dimensions with horizontal ground distance, they proposed a 2° ‘narrow zone’ projection to reduce the scale (projection) factor of the ‘grid-toground’ difference to an ‘acceptable’ limit for mathematical consistency of the grid distance dimensions stated on plans with grid distance projection coordinates.
The NSW Survey Integration proposal claimed that, with a 2°-zone projection plane, grid distance dimensions would “significantly equal” ground distance in the “vast majority of cases” and that the scale (projection) factor was within an “acceptable” limit of 1:8000. Yet, in this:
• Allowance was not made for the oftengreater height (above sea level) factor;
• Overstatement of measurement often occurred;
• Tolerance was still needed for the maximum error in measurement to not exceed 1:12,000.
However, this action to narrow the zone width to ensure that the grid distance approximated horizontal ground distance detracts from the essential issue of why grid distances need to be stated as dimensions in the first place.
4.2 Statement of mathematically inconsistent data on plans
The ‘narrow zone’ coordination practice of mathematical consistency of calculation data is used to justify the statement of grid distance dimensions on plans. This was to prevent any calculation error due to different and inconsistently stated data. Yet, unless clearly declared otherwise, confusion and error can occur when grid distance dimensions replace the more expected horizontal ground distance dimension, especially as their similar size and same mode of statement tends to hide the difference. However, dimensions and coordinates are stated differently, in different modes. In this way, both horizontal ground distance dimensions and grid distance coordinates can be shown on the same plan (with a calculable difference) and (although mathematically inconsistent) without confusion, simply by stating [1] horizontal ground distance in dimension form and [2] grid distance as coordinates and in coordinate form.
Coordinates can be stated either as or in:
1. Coordinate mode at the relevant point on the plan (and potentially in italics), or
2. An (accompanied?) schedule of coordinates referenced to relevant points, and/or
3. To dispel any confusion, a horizontal ground distance conversion statement with
a. the multiplication factor for conversion from ground to grid, and
b. the applicable static coordinate datum (e.g. MGA94 or MGA 2020), acknowledging that, for title clarity, data and statements on title plans must be kept to a minimum.
Adoption of the different modes of statement allows both ground (dimension) and projection (coordinate) data to be shown on the same plan [1] without confusion, [2] without ‘near enough’ approximate grid distance dimensions, [3] without the need for ‘grid-toground’ conversion for measurement and [4] without an additional ‘narrow zone’ coordination system.
4.3 Calculation of mathematically inconsistent data in Coordination
In ‘narrow zone’ or State Plane Coordinate Systems, either (1) grid distance is deemed ‘near enough’ for use as a dimension or (2) a ‘grid-to-ground’ conversion is applied to the grid distance when the more-precise horizontal ground distance dimension is to be determined, measured and used. However, there is another option: (3) The ‘grid-to-ground’ conversion can be made with the coordinate calculation with data conversion, becoming part of coordinate calculation; a calculation that must be made anyhow. This is supported by the six reasons outlined in the following subsections:
4.3.1 Conversion, only when required, with the obligatory coordinate calculation.
Data conversion should be carried out only when it is required, with coordinate calculations.
Grid distance and coordinates on the projection plane cannot be measured and must be calculated. Therefore, it makes sense that the data conversion should be calculated, as required, with the obligatory coordinate calculation. Ensuring that calculating data is mathematically consistent is not a problem [or issue] for the mathematically competent professional surveyor. Therefore, it seemed odd that in the 1970’s NSW Survey Integration proposal, NSW surveyors, known for precise measurement, should advocate mathematically consistency but with often imprecise, ‘near enough’ dimensions. Subsequently, this proposal was rejected in favour of mathematical consistent calculation between the stated coordinates and the stated horizontal ground distance dimension. Also, for coordinate calculation, a Combined Conversion Factor and coordinate datum were stated on all survey plans. This way, conversion with coordinate calculation has been practiced for 50 years without confusion. During this time computers and software have made the calculation almost automatic, and the use of more precise measuring equipment [(EDM) along with new techniques [GPS, GNSS, etc.] have made measurement and dimensions more precise. As a result, the mathematical consistency calculation as part of coordinate calculation and the statement of horizontal ground distance dimensions should become mandatory. Conversely, the identical, but anomalous and inexact grid distance dimension, should be deprecated.
4.3.2 Choice for ‘Grid-toGround’ conversion with the Coordinate calculation
‘Grid-to-ground’ conversion with the coordinate calculation offers a choice in calculation method and can be carried out without involving dimensions, by alternatively using [1] ‘point-topoint’ working or [2] East and North ordinates between points. This is especially relevant when comparatively few coordinates are stated or used.
4.3.3 Less risk of mistake and error There is less confusion and less risk of mistake and error when only horizontal ground distance dimensions are stated on plans than when grid distance dimensions can otherwise be stated. Apparently, there have been incidents where off-site materials, prefabricated structures and other items made in standard linear units did not fit on-site when grid distance dimensions, being identical, were stated on plans and were mistaken for the usually expected horizontal ground distance. Similarly, with only horizontal ground distance dimensions, there is not the need for ‘grid-to-ground’ conversion of grid distance for when dimensions are to be measured and used. Furthermore, there is advantage and convenience in calculation by having both grid (coordinates) and horizontal ground (dimension) data on plans with a common grid north orientation and with a statement of a Conversion Factor for calculating between them. Duplexity, mistake and error does not occur in Australian practice.
4.3.4 Functional uselessness of Grid Distance dimensions
The projection plane is assumed for the special purpose of coordinate position referencing in surveying and mapping. For convenience of calculation and mathematical consistency of stated data, grid distance dimensions and projection coordinates are shown on ‘narrow zone’ coordination projection planes. However, because stated grid distance (dimensions) vary from place to place and height to height in its conversion to horizontal ground distance (and because it cannot be actually measured at sea level), [1] it does not perform the function of a dimension in land measurement. Also, as it is not stated in coordinate form, [2] it does not perform the function of position reference. Thus, unlike horizontal ground distance dimensions and projection coordinates, which (as separate standalone entities) function in their own right, grid distance dimensions are functionally useless by themselves. To be of any use, in reality, grid distance dimensions must be multiplied by ‘grid-to-ground’ conversion for horizontal ground distance land dimensions, and by trigonometrical functions for coordination. Also, as part of the coordinate calculation, with ‘point-topoint’ or ordinate calculation, grid distance (as a dimension) is not required at all. In fact, Grid distance, if used in dimension form, is really a transitory, non-essential component in coordinate calculation.
By being the only exception to horizontal ground distance dimensions in standard linear units where measured and used, its similar ‘near enough’ size makes it not only deceptive as a dimension, but it also requires its own superfluous ‘narrow zone’ coordination system. There is no justification for this duplexity. Again, grid distance, and its “narrow zone” coordination, should never be used and it should be deprecated from surveying practice.
4.3.5 Difference between Grid and Ground Distance becomes a calculating quantity only
By stating horizontal ground distance (instead of grid distance) dimensions on plans, the matter of the “closeness” of the difference between them, and the need for ‘near enough’ grid distances and ‘narrow zone’ widths, is no longer an issue. Without the need for grid distance dimensions, the ‘ground-to-grid’ difference becomes a calculating quantity only in coordinate calculations, and so can be larger than the ‘near enough’ magnitude needed in State Plane Coordinate Systems, Low Distortion Projection coordination and other ‘narrow zone’ coordination.
4.3.6 Using any Projection Zone Width
When horizontal ground distance is stated as the land dimension, any (or just one) zone width can be used. Stated conversely, horizontal ground distance dimensions maintain their direct nexus [or mathematical consistency] with measurement without the need for ‘gridto-ground’ conversion and without it placing limits on the choice of zone widths and coordinate systems.
5. The use of the 6° UTM coordinate system
As previously mentioned in section 1.1, the 6° UTM projection coordinate system was introduced for mapping in the 1930s, was used during World War 2, and then, with the International Map of the World [IMW] mapping, is now universally used for worldwide mapping. Consequently, as any zone width can be used with horizontal ground distance dimensions, it is hard to argue against using the existing and established 6° UTM mapping system for survey coordination as well. This is supported by the four reasons outlined in the following subsections:
5.1 One Coordinate System for all land Spatial Position Reference purposes
Ideally, there should be one coordinate system for all uses. Surveying is only part of a wider application in areas such as cadastres, information systems, databases, mapping, and military and emergency location services. Although positions for these other uses may not be required to the precision of surveys, they must be underpinned by precise survey control. On the other hand, coordinate cadastre reference is only part of surveying practice. It is used for the determination and reference of unique absolute position as part of control, cadastral and boundary re-establishment surveys. In the coordinated cadastre, property surveys, boundary marks, monuments, relative position and dimensions have greater legal status, significance and substance to the surveyor (and user) than absolute coordinate values, especially as the coordinates cannot be seen. However, (GNSSderived and MGA) coordinates can supplement other evidence in the location of lost property boundaries.
5.2 Avoiding Coordinate confusion
Using only the 6° UTM coordinate system (MGA) for all coordinate and mapping purposes overcomes the need and confusion of calculating, and showing on plans and maps, State Plane Coordinate Systems, Low Distortion Projection systems and other ‘narrow zone’ coordinate systems. Apparently, such duplication and confusion occurred during the 25 years when the 2°-zone ISG [as well as 60 AMG] was used in NSW.
5.3 Overcoming the discontinuity of smaller coordinate systems
The much larger 6° by 4° UTM zone size (or 600 km by 450 km) and, with ½0 overlaps, (700 km by 550 km) overcomes the discontinuity and confusion of many smaller and/or ‘narrow zone’ coordinate systems. For instance, NSW is covered by three 6° MGA zones compared to the [used from 1975 to 1995] seven 2° ISG zones.
5.4 Allowing for ProjectSpecific survey coordination.
The use of the 6° UTM system for survey coordination does not preclude use of project-specific survey coordination at the mean horizontal ground distance plane (i.e. Low Distortion Projection coordination, centreline and cross sections, datum lines, set out for offsite prefabricated structures and other forms of coordination or survey at a height and/or orientation convenient for the project) provided that it is appropriately integrated to the 6° UTM survey and mapping coordinate system.
6. The ideal dimension and coordinate system
6.1 Ground Distance dimension – 6° UTM Survey and Mapping Coordination System
One underlying and easily overlooked reason for the adoption of the horizontal ground distance dimension – 6° UTM coordinate system in Australia was that both already existed. They just needed to be used in survey integration. This also applies worldwide. By outlawing grid distance dimensions (and phasing out its ‘narrow zone’ coordination), the 6°-zone UTM coordinate system used worldwide for mapping can also be used for survey coordination and survey integration. In Australia, the horizontal ground distance dimension – 6° UTM (MGA) system provides:
• One homogenous national datum and one common spatial data system. • A complete and unambiguous dimension and coordination system for all uses.
• Direct compatibility with Global Navigation Satellite System (GNSS) observations.
• Less confusion by not having two different dimensions and two different coordinate systems.
• Reduction in conversions required between different dimensions and coordinate systems.
• Reduction in the number of zone borders and their associated overlap issues due to the wider 6° UTM zone width.
• Compared to the duplexity of dimensions and coordinates, obvious cost savings …
The foregoing is made more realistic with the advances in surveying and measuring equipment, GNSS technology, computers and software since the 1970s (when the NSW Integrated Survey dispute occurred) and from many years before when State Plane Coordinate Systems were implemented elsewhere.
6.2 Benefits of the Australian 6° UTM Survey and Mapping Coordination System
The benefits of the Australian 6° UTM survey and mapping coordination system far outweigh its cost in comparison with also having the duplicate NSW Survey Integration proposal. The 1970s decision to continue with horizontal ground distance dimensions was incisive by avoiding the confusion and calculation with the NSW proposal’s statement of grid distance dimensions. Also, with resulting benefits, Australia converted from imperial to metric units on 1 July 1972. Yet, especially with satellite-based positioning and computer software, the major benefit was having all mapping, databases and all survey coordination unified on the one, existing 6° UTM projection coordination system. This finally occurred in 1995 when NSW adopted the Australia-wide 6°-zone MGA system. This avoided the confusion, calculation and cost of duplicate survey dimension and mapping coordinate systems. In doing so, the Australian experience shows that it is never too wise, and never too late, to benefit from the change. So, considering the reasoning in this paper, and the improvements in technology since the 1970s, it would be beneficial to make the change by banning grid distance dimensions and instead state horizontal ground distance dimensions, and by doing so, also benefit by having a coordinated cadastre and mapping system based only on the existing 6° UTM mapping projection.
7. The incongruity of having both grid and ground distance dimensions in the USA
After 130 years, [on 1/1/2023] the USA will no longer use the “US Survey Foot” as a standard unit of linear measurement. For over 60 years the US has also used the “International” Foot. The “folly” of having two nearly identical versions of the unit of linear measurement had become apparent, resulting in the confusion of dual definition, evidence of [unintended] error and costly blunders. This led to the recent bold action to deprecate the “US Survey Foot” so that the “International” Foot then becomes the only standard unit of linear measurement in the USA. In a similar context, the USA also has two nearly identical ways of stating dimensions in land surveying. Following the introduction of the State Plane Coordinate System [SPCS] nearly 90 years ago, land measurement dimensions have been stated as grid distance on the coordinate projection plane, usually at sea level, instead of [and the only exception to] the more common and usual horizontal ground distance in standard linear units where measured and used.
In SPCS2022, the surveying profession in some States of the USA raised the elevation of their projection planes above sea level to reduce the height factor in the “grid to ground” adjustment. This was to make the stated grid distance dimension closer to horizontal ground distance. However,
[1] this action actually highlights the intrinsic value of the statement of horizontal ground distance dimensions that replicate the measurement in standard linear units at its location.
[2] Further, by still having the nearly identical, variable, and different grid distance [rather than horizontal ground distance] stated as dimensions on survey plans perpetuates the similar duplexity and confusion that prompted deprecation of the “US Survey Foot”.
[3] All that’s needed is to apply the same “bold” action used to deprecate the “US Survey Foot”, to also [boldly] deprecate the statement of grid distance dimensions so that horizontal ground distances would then become the only linear dimension stated on USA survey and title plans.
8. Summary and concluding remarks
From a cadastral perspective, this paper has explained and promoted the use of horizontal ground distance dimensions and the Australian 6° UTM survey and mapping coordination system throughout the world. In summary, it has outlined in the following:
• From 1788 (and the initial settlement of NSW) the primary function of the cadastral surveyor was to physically locate and mark deed boundaries on the ground. Further, it’s the visible evidence of the property boundary in the field (and not invisible coordinates) that the public wants and the law relies upon in settling boundary disputes.
• Copied from overseas, the 1970’s Survey Integration proposal introduced survey control, the coordinated cadastre, and grid north into survey practice. However, its proposal for grid distance and 20 zone coordination was disputed, and then dismissed.
• Instead, emphasis was given to the importance of land, survey and title dimensions (horizontal ground distance) being stated in standard linear units where they are measured and used. This (and not distance down on a projection plane at sea level) is what the public wants. (The USA [and overseas] surveyor’s grid distance dimension is the only exception to this precept)
• It was explained that grid distance dimensions are functionally useless in themselves, and that their statement as an (often) deceptively approximate dimension is an anomaly, unnecessary and should be deprecated. For cadastral surveys, grid distance dimensions should not be used, ever.
• It followed that ‘narrow zone’ coordinate systems elsewhere that are based on and use grid distance dimensions should also be phased out and replaced.
• Instead, it was recommended to use the successful Australian practice (the Australian 6° UTM survey and mapping coordination system), which applies only horizontal ground distance dimensions and only 6° UTM coordination (initially AMG66, MGA94 and now MGA2020).
• As its basis (i.e. horizontal ground distance dimensions and 6° UTM coordination) already exists and is used throughout the world, this Australian best-practice could easily replace the confusion and duplication (i.e. grid and ground dimensions, “narrow zone” and 6° UTM coordination) that applies where ‘narrow zone’ coordinate systems and 6° UTM mapping are both used.
• By combining horizontal ground distance dimensions and 6° UTM coordination, one unified worldwide system of survey dimensions, coordination and mapping could be established. [Over the last 50 years EDM, GPS and the geocentric MGA maps have been introduced seamlessly into this unified system in Australia]
• Less confusion, less calculation and considerable cost savings and benefits would result from using only horizontal ground distance dimensions and only 6° UTM coordination.
All the foregoing just goes to show that you cannot take anything for granted, even with the most credible of sources and supporters. But, by ‘thinking outside the box’ in the 1970s NSW Survey Integration dispute (and with the decision of the NSW Registrar General), Australia can claim to have the best survey coordination and mapping system in the world.
9. References
Read J.R. (1975) The advantages of 6° wide zone integration over 2° narrow zone integration in Australia, Australian Surveyor, 27(1), 29-40 & Erratum in 27(4), 232, due to misplaced text by the Editor.
Read J.R. (1981) A coordinate system for North America based upon the 6° U.T.M. zone, Surveying and Mapping, 41(1), 83-87.
Read J.R. (2022) Cadastral Surveys, Ground Distance and the Australian 60 UTM Survey and Mapping Co-ordination System: the 1970’s Ground Distance vs. Grid distance Dimension Dispute. APAS 2022 Conference www.apas.org.au
This paper has been adapted from a larger paper written for a NSW surveyor readership and published in the proceedings of the APAS2022 Conference, available at www.apas.org.au.
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