# Step 4 in Map Projection: Properties of Map Projection (Preserving Metric Properties) (Especially for GATE-Geospatial 2022)

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It is known that a globe is a true representation of the earth, which is divided into various sectors by the lines of latitude and longitude.

Theoretically map projection might be defined as “a systematic drawing of parallels of latitude and meridian of longitudes on a plane surface for the whole earth or a part of it on a certain scale so that any point on the earth surface may correspond to that on the drawing.”

Metric Properties of maps

Maps are flat, but the surfaces they represent are curved. Transforming, three-dimensional space onto a two-dimensional map is called “Projection.” Map projections are necessary for creating maps. This process preserves at least one of the following properties of map:

• Shape
• Area of Map
• Distance
• Direction

### 1. Angle in Projection

A projection in which the scale, although varying throughout the map, is the same in all directions at any point, so that very small areas are represented by correct shape and bearings are correct. A projection that retains this property of angular conformity is called a conformal or orthomorphic map projection.

### 2. Distance in Projection

The problem with angular conformity is variation in distance. If our purpose in projecting a map is to accurately measure distances, we must select a projection that preserves distance. Such projections are called “equidistant projections.” In an equidistant map projection, the length of particular lines in the map are the same as the length of the original lines on the curved reference surface.

### 3. Direction in Projection

Usually equidistant maps are equal direction maps.

### 4. Area in Projection

In an equal-area map projection the areas in the map are identical to the areas on the curved reference surface that means that areas are represented correctly on the map.

## Properties of Projection: Which Metric Properties to Preserve

All mapped areas have the same proportional relationship to the areas on the Earth that they represent. A map projection is a set of rules for transforming features from the three-dimensional earth onto a two-dimensional display. No flat representation of the earth can be completely accurate, so many different projections have been developed, and each suited to a particular purpose. A map projection would preserve some of the above metric properties while compromising others.

### Rules of Projection

Map projections differ in the way they handle four properties

• No projection can preserve all four simultaneously, although some combinations can be preserved, such as Area and Direction
• No projection can preserve both Area and Angles. The map-maker must decide which property is most important and choose a projection based on that.

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