Scale is first and most important characteristic for a map. Without scale, the diagram or graphic created becomes a simple sketch.
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Definition of Scale:
Scale can be defined as the factor by which actual features on ground are enlarged or reduced for representing on a plane.
Some people also define scale as the ratio of distance measured between 2 points on map to the distance measured between the same 2 points on ground.
Types of Scale Based on Representation:
Different types of scales are used for making maps in the field of cartography. These types are simply based on the way scale is represented on the map. However, for a map prepared scale will be fixed irrespective of the way chosen for representation.
Depending on the way scale is represented, scale is classified into 3 types i.e., 1. verbal scale 2. Representative fraction 3. Graphic Scale.
Verbal scale makes use of words language for representing scale related information on the map. How much distance a unit or no of units measured on the map represents in reality is given by this scale. The distance or linear units are used for depicting this scale on the map.
For example: 1 inch = 1 Kilo meter. This is an example for verbal scale. Here the smaller distance, i.e., is 1 inch is usually the distance represented on the map. 1 Kilometer is the distance on the ground which is equal to 1 unit measured on the map.
This scale is also called as ratio scale. Instead of words, it uses the numbers or values for showing the scale. As the name says, it is represented using a fraction or ratio. This is one of the most common types of map scale used in many maps.
Example: 1: 10,000 or 1/10,000
The above representation is an example for ratio scale. It says one unit on map is equal to 10,000 units on the ground. That means all ground features are reduced by 10,000 times in order to be represented on the map.
The advantage of verbal and ratio scale are, they are very easy to interpret and understand.
The above 2 types of scales i.e., verbal and ratio scales have certain disadvantages. If the map becomes too old or stored in adverse conditions, depending on the material used for map preparation it may expand or shrunk. In such situations all distance and area measurements made from the map becomes incorrect.
The problem can be solved by using a graphic scale in the map. This scale is also called as bar scale or linear scale.
The graphic scale contains a linear bar which is divided into uniform grids along the length. Each grid represents same distance as represented on the scale. For making measurements, the length of an object or distance between 2 points is measured and compared against the scale. Depending on the value arrived from the bar, the actual ground distance is derived.
For making more precise measurements, the one of the grids will be divided into further subdivisions and the leftover length after a particular number of divisions is measured against these subdivisions.
Some people may find it difficult to use. However, it overcomes the problem of map shrinkage or expansion. Because, the graphic scale also shrinks or expands inline with the map, hence scale remains unaltered.
To overcome the difficulty, some maps are prepared including 2 different types of scales of which one will be graphic scale and other will be verbal or ratio scale.
Types of Scale Based on Value of Fraction:
This classification is based on what is the value of representative fraction used in the map preparation. Based on this, maps as well as scales are classified into 2 types.
There is no clear rule or division what should be the limit for calling a map scale as large scale. Important factor about this scale is, more details are shown in a map when large scale is used for preparation. However, less area coverage will be shown in a single map as the scale is large and more details are given.
1:500 scale map of a village shows details in a more detailed fashion compared to a map prepared at a scale of 1:25,000. Hence, 1:500 scale is considered as larger scale.
Also, One can compare the fraction values in the example to find that 1:500 is much greater than 1:25,000 and hence 1:500 is larger scale. Large scale will have less denominator value compared with small scale maps.
Small scale is exactly opposite to the large scale. For a map prepared using small scale, less details are shown as magnification is not enough or less compared with large scale maps. However, a large amount of area can be shown in a single map using the small scale.
In the above example (given in large scale) 1:25,000 is small scale.
Other than these 2 scales some people classify a 3rd type of scale which is intermediate or medium scale. This classification of scale types based on ratio value is totally dependent on the available maps and the person who is studying the maps.
Different types of maps are prepared at different scales depending on their purpose. For example, cadastral maps which shows land ownership records are prepared at a larger scale, while political maps and topographic maps of the world are prepared at a small scale.
One can read more details about different types of maps in the following article: