Maps are drawn to represent the earth as a whole or parts of it drawn to scale on a flat surface. Maps are easy to handle as they can be taken to the field. Therefore it is carried by explorers, tourists and surveyors. Generally signs and symbols in different colors are used in maps to represent the relief features, rivers, land use, vegetation and many more. One particular type of map is a topographic map. This map shows much detail about small areas. A topographic map shows much detail about relief features, rivers, land use, vegetation, settlements, roads and railway lines and administrative units and their boundaries. Maps are drawn to a scale to get the correct relative distances of places on the earth.
The scale of a map is the ratio or proportion between distances on the map and the actual distances on the ground. The scale of a map is represented in three different ways:
- A Statement or Verbal Scale expresses the proportion in words. Actually it expresses the units of the map as well as the ground.
e.g., 1 cm = 500 m, or 2 cm = 1 km.
- RF or Representative Fraction is the representation of the scale in ratio or fraction. In this fraction, the numerator is usually 1 and is the map distance. And the denominator is the ground distance.
RF = Map distance / Ground distance
Both the map distance as well as the ground distance must be of the same unit. Thus,
RF = 1 / 500,000
It means 1 cm on the map represents 500,000 cm on the ground.
The unit is generally not stated, meaning the ratio could represent accurately any unit of measurement.
- The Linear or Graphical Scale is a line of convenient length divided at regular intervals and graduated in terms of distances on the ground.
Linear scale—- 1:50,000
On a map distance between two points is measured in centimeters using the scale. The scale of the map may be used to calculate the actual distance between two points on the ground:
- If the scale of a given map is 1 cm = 2 km, and the distance between two points on the map is 5.6 cm then the ground distance between the two points is
1 cm = 2 km
Then 5.6 cm = 5.6 × 2
= 11.2 km.
- If the scale of the map is 1:50,000 then 1 cm is equal to half a km. If the distance between the places on the map is 7.8 cm, the distance on the ground between them is
1 cm = ½ km
Then 7.8 cm = 7.8 × ½ = 3.9 km
- If a linear scale is drawn on the map then the distance between the two places is placed over the linear scale and the actual distance in kilometers is read directly using the primary and secondary divisions.
DIRECTIONS ON MAPS
The location of a place is fixed by taking both distance and direction of it. These are the two vital components of a map. The direction of a place is the relative position of a place with reference to the north line.
- An arrowhead is used to represent the north direction.
- On topographical maps, the lines of longitude represent the north-south lines, and the lines of latitude, represent east-west lines.
- Four cardinal directions are found on the magnetic compass. And these are north, south, east, and west. And halfway between north and east lies the north-east, between south and east is south-east, between north and west is the north-west, and between south and west is the south-west.
REPRESENTATION OF RELIEF ON MAPS
On maps relief features are shown with the help of
- Hachures are short disconnected lines drawn along the slope. These lines do not indicate absolute height but they show the general configuration of the ground.
- Hill-shading is shown by light and shade. The dark slopes are shaded. Those on which there is light are unshaded and appear brighter. Hill-shading, however does not give any idea of the height of the land or the slope.
- Layer tinting or coloring is a method of showing relief features with the help of colors.
- Contours are the most common methods of showing height on a map. Contours are generally drawn by using lines. This method is the most accurate method. Contour lines are lines joining places having the same height above sea level. These lines are also called ‘isohytes’. The word ‘iso’ meaning same and ‘hytes’ meaning heights. The contour lines are drawn at an interval of 20 m.
Other methods of representing height on topographical maps are:
- Form Lines: these are shown by broken lines. These lines are not numbered and they show minor details.
- Spot Heights: these are shown with the help of a dot with a number to the height of that spot, e.g. 251
- Benchmark: this is used by surveyors to measure the accurate height of a place. It is written as BM 251.6.
- Triangulated Station: these represent heights above sea level and are determined by trigonometric survey. This is generally shown on the map marked by a triangle and a number beside it, indicating the height, e.g., 251.
- Trigonometrical Point: this is shown with the help of a dot and a number, e.g., 251
- Relative Height: this represents the height of a tank or sand hill or embankment. This is taken with reference to the surrounding ground level and is written as 3r beside the feature.
The exact location of a feature on map can be fixed with reference to a grid. A grid is the network of lines of latitudes and longitudes. These grid lines are drawn as red lines.
- The origin of the grid system in the south-west corner of the map.
- To find the location of any point, its distance east and north of the origin of the grid is seen.
- When giving reference to a point, the eastings are given first and the northings are given later.
- On every map, two figure eastings and northings are printed along the margins of the map at intervals of 1 km.
- The eastings increase in value eastwards, and the northings increase their value northwards.
- The four figure reference of a place is given by naming the two lines. For example, if the grid reference of a village P is 5428, it means that the village is located in the 1 km square with eastings of 54 and the northing of 28. This called the four figure grid reference.
- When locating places with a point location of spot height, temple, railway station, well, etc. a six figure grid reference is used. First the eastings is taken then the northings. Then an estimation is made of the intersecting point in terms of the subdivisions marked. The third digit is taken as the distance from the eastings of the grid square identified. The sixth digit is taken as the distance from the northings of the grid square identified.
The geological structure and relief of an area, the nature of rocks, the slope of the land and the amount of rainfall experienced, all are reflected through the flow of the main river and its tributaries. This arrangement and form of streams thus formed is called the drainage pattern. The important drainage patterns are:
1.Dendritic Pattern: This pattern looks like a tree. It is the most common pattern. The small tributaries of a river meet the larger streams at an acute angle.
2.Trellised Pattern: It is often found that due to alternating bands of hard and soft rocks, the streams and tributaries meet the main river at right angles, forming a trellis. This pattern is also called the rectangular drainage pattern.
3.Radial Pattern: Streams that radiate out from a focal point, generally, form this type of pattern. The focal point can be peaks, particularly conical peaks. The streams in such a case drain outwards in all directions.
4.Disappearing Drainage: Sometimes the streams do not join the main river but disappear into the soil due the sandy nature or porosity of the soil. Sometimes the streams may also disappear because of its insufficient water. This pattern of drainage is usually found in arid regions.
A cluster of inhabited houses make the settlement patterns. They are classified on the basis of their size, shape, pattern, and also whether they are rural or urban.
1.Dispersed or Scattered Settlements: Generally in hilly areas where population is very less, this type of settlement is found. In such a pattern the houses are far from each other and may also be isolated.
2.Clustered or Nucleated Pattern: This is a compact settlement pattern where the houses are permanent and form cluster. These types of settlements are found in fertile plains where ample water is available.
3.Linear Settlements: When permanent houses or huts are built alongside a river bank or road or railway lines or even along coastal areas, the pattern that emerges is like a ribbon or linear.
4.Radial Pattern: In this pattern, the houses are clustered in a star like pattern around a tank, a lake or a road junction.