A map is a representation or a drawing of the earth’s surface or a part of it drawn on a flat surface according to a scale. But it is impossible to flatten a round shape completely.
Maps provide more information than a globe. They are of different types. Some of them are described below.
1. PHYSICAL MAPS
Maps showing natural features of the earth such as mountains, plateaus, plains, rivers, oceans etc. are called physical or relief maps.
2. POLITICAL MAPS
Maps showing cities, towns and villages, and different countries and states of the world with their boundaries are called political maps.
3. THEMATIC MAPS
Some maps focus on specific information; such as road maps, rainfall maps, maps showing distribution of forests, industries etc. are known as thematic maps.
Suitable titles are given on the basis of information provided in these maps.
4. CADASTRAL MAPS
Town maps and village maps; showing details of streets, plots and fields in the area.
The scale of the map is the ratio of proportion between the dimension on the map and the actual dimension on the earth.
Scale of map may also be indicated by a fraction called the Representative Fraction (RF) in which numerator is 1.
R.F of a map = Distance on the map
Distance on the ground
The R.F of a map may be indicated as 1/ 100,000 or 1 : 100,000. This means one unit of distance on the map is equal to 100,000 units on the ground.
Maps are divided as large-scale maps and small scale maps on the basis of scale. The topographic map which is on a scale of 1: 50,000 is a large scale map. In a large scale map small areas are representative on a large size map. Wall map is a small – scale map. It shows a large area on a small size map.
REPRESENTATION OF RELIEF FEATURES
In cartography, a contour line joins points of equal elevation (height) above a given level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines.
More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value. The gradient of the function is always perpendicular to the contour lines. When the lines are close together the magnitude of the gradient is large: the variation is steep. A level set is a generalization of a contour line for functions of any number of variables.
Contour lines are curved or straight lines on a map describing the intersection of a real or hypothetical surface with one or more horizontal planes. The configuration of these contours allows map readers to infer relative gradient of a parameter and estimate that parameter at specific places. Contour lines may be either traced on a visible three-dimensional model of the surface, as when a photogrammetrist viewing a stereo-model plots elevation contours, or interpolated from estimated surface elevations, as when a computer program threads contours through a network of observation points of area centroids. In the latter case, the method of interpolation affects the reliability of individual isolines and their portrayal of slope, pits and peaks.
Elevation and depth
Contours are one of several common methods used to denote elevation or altitude and depth on maps. From these contours, a sense of the general terrain can be determined. They are used at a variety of scales, from large-scale engineering drawings and architectural plans, through topographic maps up to continental-scale maps.
"Contour line" is the most common usage in cartography, but isobaths for underwater depths on bathymetric maps and isohypse for elevations are also used. The process of drawing isohypse contour lines on a map is called isopletion.
In cartography, a contour interval is any space between contour lines, representing a difference in elevation between the lines. When calculated as a ratio against the map scale, a sense of the hilliness of the terrain can be derived.
If contour lives are closer, it indicates a steep slope; gentle slope is indicated when contours are widely spaced.
CONVENTIONAL SIGNS AND SYMBOLS (ADOPTED BY SURVEY OF INDIA)
It is the third important component of a map. It is not possible to draw on a map the actual shape and size of different features such as buildings, roads, bridges, trees, railway lines or a well. So, they are shown by using certain letters, shades, colours, pictures and lines. These symbols give a lot of information in a limited space. With the use of these symbols, maps can be drawn easily and are simple to read. Even if you don’t know the language of an area and therefore cannot ask someone for directions, you can collect information from maps with the help of these symbols. Maps have a universal language that can be understood by all. There is an international agreement regarding the use of these symbols. These are called conventional symbols.
Various colours are used for the same purpose. For example, generally blue is used for showing water bodies, brown for mountain, yellow for pleatue and green is used for plains.
There are four major directions, North, South, East and West. They are called cardinal points. Other four intermediate directions are north-east (NE), southeast (SE), south-west (SW) and north-west (NW). We can locate any place more accurately with the help of these intermediate directions.