Step 3 in Map Projection: Choosing Scale of Projection (Especially for GATE-Geospatial 2022)

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A globe is the only way to represent the earth with constant scale throughout the entire map in all directions. The scale of a map indicates how much the Earth has been reduced for reproduction on that map. Choosing scale of projection is further divided into two aspects:

  • Type of scale
  • Measurement of scale

Types of Scale

Scale is the relationship between the distance shown on a map and the actual distance that it represents on the Earth.

A scale is any series of items that are arranged progressively according to value or magnitude, into which an item can be placed according to its quantification.

There are three types of scale:

This Diagram Shows Types of Scale

Ration or Representative Fraction (RF) Scale

A ratio indicates how many units on the earth՚s surface is equal to one unit on the map. It is represented as 1/100,000 or 1: 100,000 means one centimeter on the map equals 100,000 centimeters on the earth.

Example: R. F. (Representative fraction)

Verbal Scale

A scale represented as a “1 inch equal to 63369 inches” is called Verbal scale. If the map is reproduced by a method such as photographing and the size of the map is modified.

Example: 1-inch equals 1 mile

Graphical Scale

A graphical scale is a ruler printed on the map and is used to convert distances on the map to actual ground distances.

Example:

This Image Shows Exmaple of Graphical Scale

Measurement of Scale: Principle Scale and Scale Factor

  • An obvious scale change converts the actual globe to a reference globe. Then the reference globe is projected into two-dimension surface.
  • When we reduce the scale from the actual globe to its reference globe, we change the representation fraction to reflect this scale change. The representative fraction for the reference globe is called the “Principle scale.”
  • Principal scale is calculated by dividing the earth՚s radius by the radius of the globe.
  • After calculating the principle scale, the next step is to calculate scale factor.
  • The ratio of the length of the scale drawing to the corresponding length of the actual object is called as Scale Factor (e. g. actual scale/principal scale)
Illustration 2 for Measurement_of_Scale_Principle_ …

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