Cartography and the essentials of map making

Detail

What cartography is

• Cartography is the art, science and technology of making maps. It also covers studying and using maps.
• Art: the map must look clear and pleasing.
• Science: it must be accurate, using measurement and mathematics.

• Technology: the tools used to draw and print it, from pen and ink to computers.

• A map is a simplified drawing of the whole Earth, or a part of it, on a flat surface, drawn to scale.

• A cartographer is the person who makes maps.

A short history: from clay tablets to digital maps

• Babylon (Mesopotamia, present-day Iraq)
• Babylonians drew maps on clay tablets. The oldest ones found date to about 2300 BCE [9].
• Most early Babylonian and Egyptian maps had practical uses, such as marking land boundaries. Few tried to show the whole Earth [9].

• The Babylonian world map (about 600 BCE) is a clay tablet with Babylon at the centre. It shows other places as circles and has notes in cuneiform (the wedge-shaped writing of Mesopotamia) [8].

• Claudius Ptolemy (about 100–170 CE, worked in Alexandria, Egypt)

• He wrote the Geographia in the 2nd century CE. It contains a gazetteer (a list of places with their positions) and a guide to drawing maps [7].
• He used latitude and longitude to fix places on a map. He also gave a way to show the round Earth on a flat sheet, which was an early form of projection [8].
• Standard editions had 26 regional maps (10 of Europe, 4 of Africa, 12 of Asia) and one world map [7].

• More than 40 editions were printed in Europe between the 15th and 17th centuries, so his ideas shaped mapmaking for centuries [7].

• Survey of India (SoI), 1767

• The SoI traces its origin to 1767, when Major James Rennell was made Surveyor General of Bengal [3].
• It is the oldest scientific department of the Government of India. Its headquarters is at Hathibarkala Estate, Dehradun (Uttarakhand), and it works under the Department of Science & Technology (DST) [2].
• The Great Trigonometrical Survey (GTS) was led by William Lambton and Sir George Everest in the 19th century. It laid the base for scientific mapping of India [3].
  • Trigonometrical survey: measuring a chain of triangles from fixed points to find exact positions and heights.
• The GTS chains run north–south and east–west across India. They are counted among the best geodetic control series in the world [2].
  • Geodetic control: a network of very accurately fixed points that all other maps are tied to.

• The SoI grew from 5 directorates (1950) to 22 directorates in almost every state [2].

• The digital age

• In the late 1980s the SoI set up three Digital Centres to build a Digital Topographical Database for the whole country [2].
• Bhuvan (Sanskrit for "Earth") is ISRO's geoportal, built at NRSC, Hyderabad. Anyone can use it to view satellite images and download satellite data for free. Government departments also host their own map applications on it [6].
• Guidelines on geospatial data (2021) freed the sector. Indian firms can now collect and make maps without prior approval [5].
• The National Geospatial Policy 2022 was notified on 28 December 2022 [4].
  • Licences, prior approval and security clearance for maps inside India are gone. Self-certification (the maker declares that it follows the rules) takes their place [4].
  • SoI data and other publicly funded geospatial data are treated as a public good, meaning they should be easy for everyone to get [4].
  • One goal is a high-resolution topographical survey and mapping system and a highly accurate Digital Elevation Model (DEM) for the whole country by 2030 [4][10].
  • DEM: a digital grid that stores the height of the land at each point.

The five essentials of map making

Every map passes through the same five steps, in this order:

Step	What it means	Key point
1. Scale	The ratio between a distance on the map and the real distance on the ground	The first decision. It limits how much detail the map can show and how real it looks
2. Projection	Turning the curved geoid onto a flat surface	Some error in direction, distance, area or shape cannot be avoided
3. Generalisation	Choosing the data and simplifying it	Depends on the map's purpose and scale
4. Design	Planning how the map looks	Symbols, lettering, colours, layout
5. Construction and production	Drawing and printing the map	Has moved from pen and ink to computers

Step 1 — Scale: the first decision

• Map scale is the ratio between a distance on a map and the matching distance on the ground.
• It is decided first because it controls everything after it:
• Large scale (for example 1:10,000) covers a small area, so it can show a lot of detail and looks close to reality.

• Small scale (for example 1:1,000,000) covers a large area, so it shows less detail and looks less real.

• Fig. 1.3 (Effect of Scale on Mapped Information) shows the same area at different scales. As the scale gets smaller, features are dropped or merged.

• Scale can be written in three ways: a statement of scale (for example "1 cm represents 1 km"), a representative fraction (RF) (for example 1:100,000), or a graphical (bar) scale.

Step 2 — Projection

• The geoid is the true shape of the Earth. It is nearly a sphere but slightly flattened at the poles and uneven.
• Map projection is the method of turning this curved surface into a flat one (a plane).
• A curved surface cannot be flattened without stretching or tearing it.
• So every map has some error in direction, distance, area or shape.
• A cartographer picks the projection that keeps correct the property that matters most for the map's purpose (detail in map-projections).

Step 3 — Map generalisation

• Map generalisation means choosing only the information the map's purpose needs, then simplifying it so the map stays clear and does not lose its look.
• The purpose decides what is selected:

Map type	What it shows	Example
General-purpose map	Many features together: relief, drainage, vegetation, settlements, transport	Topographical sheet, atlas map
Special-purpose (thematic) map	One theme only	Population density, soils, rainfall

• The scale decides how much it is simplified:
• Smaller scale → less space on paper → more generalisation is needed.
• Houses shown one by one at a large scale merge into one settlement symbol at a small scale.
• A winding stream is drawn as a smoother line, and its small bends are dropped.
• Small features (lanes, small ponds) are left out altogether.

Step 4 — Map design

• Map design is planning the graphic look of the map. It covers:
• Symbols: their size and form (points, lines, areas).
• Lettering: the style and size of names.
• Line widths: for example, a highway is drawn thicker than a village road.
• Colours and shades: for example, blue for water, green for vegetation, brown for relief.

• Layout: where the title, legend, scale and north arrow go.

• Map legend (key): the box that explains what the map's colours, shades and symbols mean.

• It usually sits at the lower left or lower right of the map.

• The same rule applies to thematic maps. Title, legend and direction are basic design parts of every thematic map.

• North arrow: shows the direction of north so the map can be read the right way round.

Step 5 — Construction and production

• Old method: drawing by hand with pen and ink, then mechanical printing.
• Modern method: computer-assisted mapping and photo-printing.
• Today: maps are built digitally from satellite images and GIS layers (see remote-sensing-gis).
• GIS (Geographic Information System): a computer system that stores map data as separate layers (roads, rivers, soils) that can be switched on, combined and analysed.
• Examples in India: SoI's Digital Topographical Database [2] and ISRO's Bhuvan geoportal [6].

Prelims Hooks

• Cartography = art + science + technology of making maps, and of studying and using them.
• Correct order of the essentials of map making: Scale → Projection → Generalisation → Design → Construction and production. Scale is the first decision.
• Projection always leaves some error in direction, distance, area or shape, because the curved geoid cannot be flattened without it.
• Trap: smaller scale = more generalisation, not less. Houses merge into one settlement symbol and streams are smoothed.
• A population-density map is a special-purpose (thematic) map. A map showing relief, drainage, vegetation, settlements and transport is a general-purpose map.
• The map legend (key) usually sits at the lower left or lower right.
• Survey of India: founded 1767 (James Rennell, Surveyor General of Bengal); headquarters Dehradun; works under the DST; the oldest scientific department of the Government of India [2][3].
• The Great Trigonometrical Survey is linked with Lambton and George Everest [2][3].
• Ptolemy's Geographia (2nd century CE, Alexandria) used latitude and longitude [7][8]. The Babylonian world map (about 600 BCE) puts Babylon at the centre [8].
• Bhuvan = ISRO's geoportal, built by NRSC [6]. National Geospatial Policy notified on 28 December 2022 [4].

Mains Points

• Scale and generalisation decide what a map can be used for.
• Large-scale maps (cadastral and topographical) suit village land records and local planning.
• Small-scale maps (atlas and wall maps) suit regional and national planning.

• A wrong scale either hides key features or crowds the map with too much detail (GS-I).

• Mapping has always been a tool of government.

• Babylonian maps were drawn mainly to mark land boundaries [9].

• The Survey of India (1767) and the GTS gave the geodetic base for revenue, railway, irrigation and defence planning [2][3].

• Digital cartography and open data are changing how maps are made.

• The 2021 guidelines and the National Geospatial Policy 2022 replaced licences with self-certification and treat public map data as a public good [4][5].
• Bhuvan offers free satellite data and hosts government applications for asset mapping, monitoring and disaster services [6].

• Together these help infrastructure planning, disaster management and land records (GS-III).

• Projection distortion has practical effects. No flat map is error-free. So the choice of projection must match the use: equal-area projections for distribution maps, and projections that keep direction true for navigation.