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Topographical mapping

Jul 2007 | Comments Off

	A historical perspective

SOME of the earliest known maps were made in Iraq which was drawn during 2400 BC for the purpose of land taxation. A Roman map dating 350 AD showed such topographical features as roads, cities, rivers and mountains. Although the basics of land surveying were known but the large scale maps before 16th century were limited to cities and other small areas. Up to the middle of 16th Century, there was little real knowledge of the geography of the most part of the world.

In 1539, a Dutch mathematician and geographer described the concept of triangulation, which became one of basic technique of field surveying and mapping and is still used today. One of the first large mapping project using triangulation was started in France in 1670 by Cassini. After a century of work by Cassini, his son, grandson and great grandson and their teams, France became the owner of first topographical map series for the entire country. It was published in 1793 as Carte de Cassini. The concept of contour line to show different elevations on the map was developed by a French engineer in 1791 and it became popular after 1850.

Background

A topographical map is two dimensional representations of three dimensional land surfaces through a combination of contour lines, symbols and texts. Topographical maps portray the shape and location of mountains, forests, rivers, lakes, cities, villages, roads, rails, bridges and most of other natural and manmade features existing on surface of earth. They also contain reference systems like graticule lines, grids, benchmarks, magnetic declination etc. Topographical maps are used by defence forces for planning operations as well as by administrators, civil engineers, natural resources managers, town planners, emergency service agencies, outdoor enthusiasts, historians, geographers etc.

Establishment of topographical mapping agencies

Real interest in topographical mapping was created when nationalism began to develop as a potent force in Europe and these countries began to undertake detailed topographical survey. At the same time European countries started colonizing the other parts of the world. They gave importance to topographical mapping, as it was required for accessing and controlling the new areas. National Mapping Agencies in some form or the other were established in most of the countries during 18th and 19th centuries. In India the Surveyor General of Bengal was appointed in 1767 and Surveyor General of India was appointed in 1815.

Methodology of surveying and mapping

Early methods

Mapping the untrodden country was a difficult and hazardous task. Extreme challenges awaited the mapping pioneers. Travel was arduous and costly. Many locations could be reached by traveling for months after crossing large rivers, high mountains, forests full of wild animals and hostile tribes. Furthermore surveying and mapping instruments were crude by today’s standards and difficult to carry. Origin of control was fixed by observing the stars. Initial base line was measured and the control was extended by triangulation. Most maps were made using a classic mapping technique called plane-tabling. The maps were reproduced by hand drawing or by copper engraved printing technique. Maps around 1:250,000 were generally prepared during this period.

Methods during last century

Some sorts of maps or charts were available to surveyors to plan their work. Most of the countries extended the triangulation series throughout the country to bring all maps on uniform reference system. Similarly leveling lines were started from coasts. Heights above mean sea level were given as benchmarks. Detailed survey was still carried out by plane tabling method. After 1930, overlapping aerial photographs revolutionized the mapping technique. Detailed survey was done in office by photogrammetric methods, which was subsequently verified on the ground. After that, map was cartographically fair drawn and printed on offset printing machines. Producing an accurate topographical map was still a long and complex process. It used to take about ten years from planning to finally printing the map. This process required a team of dedicated professionals and a series of closely coordinated steps. Maps from 1:24,000 to 1:100,000 scales were generally prepared during this period.

Modern methods after 1990

After 1990, digital mapping techniques revolutionized all stages of map production. Now the control points are provided by GPS/GNSS. Digital photogrammetry can automatically or semi automatically extracts contours and other details. Field verification can be done on palmtops/laptops by easily inserting or deleting details. Map finishing can be done semi automatically by using patterning software and colorful maps can be printed by CYMK techniques. Several complex processes required for printing a map by conventional techniques are no more required. Many countries have fully switched over to modern methods whereas some countries are struggling to produce desired results with the help of new technology.

Some interesting facts about topographical mapping

Underestimation of efforts needed to produce topographic maps

An interesting fact was noticed that almost all countries initially underestimated the time frame required to complete the topographic survey on the selected scale. For example India decided in 1905 to complete the topographic mapping at one inch equal to one-mile scale within 25 years with revision cycle of 25 years. But it took 75 years to complete the series with revision cycle of more than 25 years. Similarly topographic mapping projects were delayed in USA, France, Sweden, Australia, China, Brazil etc.

Restriction in access of topographical maps

Once the importance of topographical maps was realized for accessing and controlling the new areas, colonial powers restricted the access of such maps to prevent it falling in the hands of hostile powers. During the World War I and World War II, the restriction policies were given more teeth.

After Second World War topographical maps and aerial photography were extensively used for developmental activities and rebuilding the nations. Considering the importance of these maps as well as aerial photography for such activities, countries like USA, UK, Germany, France, Switzerland etc. removed almost all restrictions on their use. However, the civilian editions of thesemaps do not depict sensitive details like nuclear plants, defence installations etc.

Availability of topographical information from various sources

Now with the availability of highresolution stereo satellite imageries, information about topography of all parts of world is known and openly available unlike in previous centuries. In fact Google-earth depicts almost all major towns with high-resolution satellite imagery. Anyone having the internet connection can take a virtual world tour of major cities and tourist places in the world. He may also see beautifully laid out aerodromes, nuclear plants, magnificent buildings, his own house and surrounding area etc. Many people are arguing if geographical information cannot be denied to adversaries; why not use it freely for own development. Therefore many countries are reviewing the pros and cons of map restriction policies.

Spatial Data Infrastructure

Many government and private organizations had created geo-spatial data for their own use during the last few decades for economic activities. It resulted in geo-spatial data explosion and often duplication of efforts. To avoid duplication of efforts and take full advantage of already created data, many countries have created an organization known as National Spatial Data Infrastructure (NSDI ). Well defined standards are being developed for Spatial Data infrastructure (SDI ) at national and international level to give information about the quality & availability of various type of geo-spatial data as well as to facilitate data exchange. However, it has been noticed that unless participating agencies cooperate whole heartedly, NSDI can not achieve the desired results.

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	A historical perspective

Development of topographical maps in some countries

USA, Australia and China are chosen for case studies, being large countries.

USA

In 1807 President Jefferson established the ‘Survey of Coast’ that was renamed in 1836 as ‘US Coast Survey’ and 1878 ‘US Coast and Geodetic Survey’. This organization surveyed the area near the coast line till 1878. In the meantime the mapping of interior of county was done by several organizations including ‘Army Corps of Topographical Engineers’. First maps were generally drawn by hands. Different groups were working in uncoordinated way. Therefore US Geological Survey was established in 1879. USGS started with topographic survey on various scales from 1:24,000 to 1:250,000. But the object of complete coverage could not be achieved by target year of 1925.

Thereafter the National Topographical Program was introduced in 1939. This legislation laid down the specifications for the National Topographical Map Series and appropriate standards of map accuracy. Based on this programme 1:24,000 scale (except deserts), 1:62,500 scale (in Alaska 1:63,360) and 1:250,000 scale surveys were adopted. USGS began using aerial photographs to produce and update maps since 1930s.

By 1947 maps at the scale of 1:24,000/1:62,500 covered only 25% of USA but by 1968 this had been increased to 78%. In 1976, national coverage at 1:24,000 was 68% complete and about 80% of the Alaska (at 1:63,360) had been covered. By that time many countries including India had almost complete coverage on 1:50,000 scale.

In order to speed up the revision of existing map sheets, an interim revision was introduced in 1967. Extensive and important topographical changes were overprinted in purple on exiting maps by using aerial photography but without field check.. In 1975, it was decided that for all areas not yet covered by traditional 1:24,000 scale sheets, orthophotoquads (rectified photographs with important details, names grid/graticule and marginal items etc) should be produced especially for deserts and less developed areas.

As it became evident that complete coverage by traditional maps at 1:24,000 scale could not be achieved before the end of century, manuscript maps without cartographic fair drawing have been printed since 1982.

Based on the Metric Conversion Act of 1975 a modification of official topographic maps of the USA was made to confirm to the metric system. In the 1980s, the use of computer to scan, redraw and publish the maps significantly reduced the time required to update maps in areas of rapid growth. A new series on 1:100,000 scale was published which was compiled from 1:24,000 scale maps. Some states adopted 1:25,000 scale after adoption of metric system.

Now the complete country except Alaska is covered by more than 55,000 sheets produced on 1:24,000/1:25,000 scale and Alaska is covered by 2,700 sheets on 1:50,000 scale. In addition complete topographic coverage of USA is also available at 1:100,000 scale and 1:250,000 scale. Most of the data is now available in digital form. Maps or data can be obtained by anyone without any restriction. USGS provides topographical maps, orthophoto maps and aerial photographs in the entire USA online for nominal charges. This data is also available from various websites e.g. topozone.

There is demand for complete and up to date topographical information. For a country of the size of USA , it is huge task even with the latest technology. Therefore to meet this requirement, USGS has started ‘The National Maps Corps Volunteer Programme’. Any citizen having a GPS receiver can become the volunteer for a selected part of the country. He will provide GPS data and information about new details. After validating the information, the USGS staff will update the topographical database. Now USGS is expecting that the changes in topographical data will be captured and integrated with the existing data in a process of continuous update, rather than through cyclical revision of 10 to 20 years. They expect that currentness of the data will be measured in months and not in years and decades.

China

China also underestimated the efforts needed to produce the topographical maps and in 1903 they originally targeted to produce a map series at 1:25,000 scale. But this proved impossible due to the insufficiently advanced state of available technology and the enormous geographical extent of the country. In 1914 it was decided to generate mapping at 1:50,000 and 1:100,000 scale as an alternative. Preparation of these series was interrupted due to outbreak of World War I. Moreover sheets produced prior to that, were strongly criticized because of their general inaccuracy. In 1928 a revised programme was introduced by the newly created Central Bureau of Land Survey (CBLS). Triangulations commenced in 1930 and from 1932 photogrammetric techniques were used for topographical survey. Tremendous efforts were made but the progress suffered because of civil conflicts and the war between China and Japan. Till then, the scales employed were 1:25,000, 1:50,000, 1:100,000 and 1:2,50,000. When People’s Republic of China was established in 1949, a new survey of China was undertaken because original base materials were transported to Taiwan by the previous government. Approximately 8000 sheets of 1:50,000 series had been produced which covered about a third of the country. However these were of somewhat inconsistent quality.

In 1956 a new National Bureau of Surveying and Mapping (NBSM) was set up. This employed the Bejing coordinate system of 1954. The control work was finished by end of 1978. The sheetline, numbering methods and symbolization of topographic maps were standardized which were similar to former USSR. Following series were used.

1. 1:25,000 For large towns and industrial zones.
2. 1:50,000 For other populated areas
3. 1:100,000 For desert and high mountains.

The NBSM expanded & became fully operational in 1973. It implemented an extensive revision programme for medium scales. In 1982 three large Bureaus together with numerous provincial Bureaus were setup and passed to Ministry of Urban & Rural Construction and Environment Protection. At that time about 80,000 personal were involved in various aspects of mapping. Priority was given to the large-scale surveys which resulted in the production of sheets at 1:10,000 and also photomaps. Even larger scales had been adopted for major towns in certain cases. By 1990 approximately 1,65,000 sheets on large scales covering built up areas had been completed. It also finished the topographical mapping of the entire country on 1:50,000/1:100,000 scales.

China has adopted digital technology since 1990 for converting the maps in digital form. National Topographical Data Base on 1:50,000 scale was created in 2005. This task involved 10,000 people from 100 different organizations. It was coordinated by NBSM and was completed in eight years. Besides vector data, this dataset includes raster maps, imageries (including 1m resolution imageies for cities), terrain, landcover and meta-data.

Chinese topographical maps except general-purpose geographical maps and tourists maps are generally not available to general public. The government is providing geo-spatial data to the industry on need base.

Australia

In Australia topographic mapping was undertaken by Commonwealth and State government mapping organizations. In 1945 National Mapping Council was created by agreement between the Commonwealth and State governments. Its function was to co-ordinate Commonwealth and State mapping activities. In 1966, metric scales were introduced.

By 1967 the whole of Australia was covered by aerial photography for the first time. The medium scale contoured mapping covered a reasonable area. In year 1968, 1:250,000 scale planimetric map series was completed. Relief on this sereies was generally shown by spot heights and hill shading. However 20% sheets were contoured.

In 1967, compilation of 1:100,000 scale National Topographical Map Series (NTMS) commenced. Relief was generally depicted by 20 meter contours. It was published by Commonwealth Government with some assistance provided by the States. There are 3065 sheets in this series. Compilation of this series was completed by 1988. Initially the publication programme had been restricted to 1646 sheets along with the coastal margins of the continent and island state of Tasmania. The interior of the continent was compiled at 1:100,000 scale but published at 2,50,000 scale. This was completed by 1986.

In 1975 the publication of the 1:2,50,000 scale National Topographic Map Series commenced. Sheets in this series depict contours at 50 meters interval. The 1:2,50,000 scale NTMS is published to civilian specifications and a parallel 1:2,50,000 scale Joint Operations Graphic series is produced for defence requirements. All of the 541 sheets required at this scale were completed by 1989 in both the series.

Now topographic maps at scales of 1:50,000 and 1:25,000 are produced by Commonwealth and State government mapping organizations. Coverage at these scales is generally confined to the closer settled areas and other places of specific interest. The State mapping organizations also undertake mapping at scales of 1:10,000 and larger for cities and other fast developing areas.

Now Geoscience Australia is responsible for producing topographic map products with a national coverage. The NATMAP product brand refers to Geoscience Australia’s new 1:100,000 and 1:2,50,000 scale paper map products. The GEODATA product brand refers to its structured digital GIS and mapping data product at scales between 1:2,50,000 and 1:1 million. Now 1:2,50,000 is the largest scale at which National Digital Topographic Data Base exists for entire continent. It is available in different themes and contains a number of feature classes. Large-scale digital data is available for developed areas. Most of the digital products are priced and are licensed for use and available to users without any further restriction.

Conclusion

Topographical mapping evolved as one of the tools of colonial powers to serve their interest. Afterwards it became essential for armed forces for planning and execution of their operations. This brought the attribute of ‘secrecy’ attached to it during 18th, 19th and early 20th century.

Applications of topographical maps for developmental activities had started gaining importance from last century. Independent experts calculated that around 10% of Great Britain’s economic activity is dependent on Ordnance Survey ( NMA) data. It is about 136 billion pounds worth of economic activity in Britain.

With the advent of GPS, total stations, digital photogrammetry, digital cartography etc. all the stages of map making have become automatic, very easy, flexible and fast. Now the demands of user community is also changing. They want multilayered, current, complete, consistent and accurate data on larger scale, tailored for their use. Therefore concept of National Spatial Data Infrastructure is being developed in many countries.