Topographical mapping

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.