Components of a map
A map should include the following components namely, the title, scale, direction, grid system, projection, legend, conventional signs and symbols.
It indicates the purpose or theme of the map. Example: India – Physical, World – Political, Tamil Nadu – Transport.
Scale makes it possible to reduce the size of the whole earth to show it on a piece of paper. A scale is a ratio between the actual distance on the map to the actual distance on the ground. Scales can be represented in three methods. They are the Statement, Representative Fraction (R.F) and Linear or Graphical scale methods.
The statement scale describes the relationship of map distance to ground distance in words, such as one centimetre to ten kilometres. It is expressed as 1cm = 10 km.
It describes the proportion or ratio of the map distance to ground distance. It is usually abbreviated as R.F. It is stated as 1/100000 (or) 1:100000. This means that one unit on the map represents 100,000 of the same unit on the ground. This unit may be an inch or a centimetre or any other linear measurement unit. Thus,
Representative Fraction (R.F.) = Distance on the map / Distance on the ground
For example: To find the RF when the scale is 1 cm to 1km. Here, 1 cm =1 km
According to the formula, R.F= 1 cm / 1 km
Convert the km to cm. Therefore, 1km =100000 cm. So, RF. is 1:100000.
Find the R.F. when the scale is 1 centimetre to 2 kilometre.
Linear (or) Graphical scale
In a map, a linear scale is represented by a straight line divided into equal parts (Primary and secondary) to show what these markings represent on the actual ground. This scale helps in the direct measurement of distance on the map.
Linear scale model
Maps are drawn normally with north orientation. North direction in a map is always towards the North Pole of the earth. If you position yourself looking at the North Pole, on your right will be the east; your left will be the west; at your back will be south. These four main directions are called the cardinal directions. Direction is usually indicated on a map by a North-South line, with the North direction represented by an arrow head.
The location of a place can be simply defined by its latitude and longitude. In normal practice, latitude is stated first and then comes the longitude. The latitude and longitude of a place can be expressed in units of degree, minutes and seconds.
A grid is a set of lines with alphanumeric codes for defining a location on a map in many topographical sheets. The lines that run horizontally from left to right of the map are known as northings, whereas, the lines that run vertically from the top to the bottom of the map are called eastings. The points at which the vertical and horizontal lines of the grid intersect are called coordinates which are identified by numbers or letters.
A map projection is a way of showing the spherical shaped earth on a flat piece of paper. Where does the word 'projection' come from? Imagine a clear globe with latitude and longitude lines and the outlines of the landmasses on it. Suppose there was a light bulb inside the globe. If you wrapped a piece of paper around the globe and turned on the light bulb, the outlines of the grid and landmasses would be projected onto the paper. Map projection is defined as the transformation of spherical network of latitudes and longitudes on a plane surface. Projections are drawn to maintain the shape, area and directions.
The three methods in widest use are as follows:
· Projection on the surface of a cylinder
· Projection on to the surface of a cone
· Projection directly onto a flat plane, called planar or zenithal or azimuthal projection
The legend of a map helps to understand the map details which are placed at the left or right corner at the bottom of the map.
A map is a global language and it needs to be drawn according to the international standards. Conventional signs and symbols are standard symbols used on a map and explained in the legend to convey a definite meaning. The topographic map contains a variety of information about physical and cultural features. These are shown by using signs and symbols in various colours so that the clarity of the map is maintained.
There are three types of map symbols
1. Point Symbols - buildings, dipping tanks, trigonometrical beacons
2. Line Symbols - railways, roads, power lines, telephone lines
3. Area Symbols - Cultivated lands, ponds, orchards and vineyards
The following colour codes are used with map symbols
1. Brown: land or earth features - contour lines, eroded areas, prominent rock outcrops, sand areas and dunes, secondary or gravel roads
2. Light Blue: water features - canals, coastlines, dams, lakes, marshes, swamps and levees, ponds, rivers and water towers.
3. Dark Blue: national waterways
4. Green: vegetation features - cultivated fields, golf courses, nature and game reserve boundaries, orchards and vineyards, recreation grounds, woodland
5. Black: construction features - roads, tracks, railways, buildings, bridges, cemeteries, communication towers, dam walls, excavations and mine dumps, telelphone lines, power lines, windpumps, boundaries
6. Red: construction features - national, arterial and main roads, lighthouses and marine lights
7. Pink: international boundaries