Map Projections: Types, Functions, and Uses in GIS with GPS

Map Projection

A map projection is a system of ordered correspondence between points on the curved surface of the Earth and a flat surface. These points are located on a network of meridians and parallels, in the form of a mesh (creating a series of distortions). Good projections must have two characteristics: to retain the areas (equivalence) and retain angles (conformity). Depending on which point is considered the center of the map, it is distinguished between:

• Polar projection: The center is one of the poles.
• Equatorial projection: The center is the intersection between the Equator and a meridian.
• Oblique or slanted projection: The center is any other point.

Functions of the Projections

Conformal Projections

A map projection is conformal when it maintains the angles formed by two lines on the surface. Such projections are used in charts.

Equivalent Projections

A map projection is equivalent when the map areas are kept the same, although the figures are no longer similar. They are generally used in thematic or parcel maps.

Equidistant Projections

A map projection is equidistant when it maintains the distance between two points on the surface (distance represented by the arc that connects them).

Aphylactic Projections

A map projection is aphylactic when it does not preserve angles, surfaces, and distances, but the distortions are minimal.

Azimuthal or Planar Projections

These are obtained by projecting the Earth's surface from a point called the vertex of projection onto a plane tangent to a point on the Earth called the center of projection. The projection maintains its geometric properties around the center of projection, and distortion increases as we move away from that point.

Advantages of UTM

The UTM projection system has the following advantages over other projection systems:

• Preserves angles.
• It distorts the surface in large quantities (below the 80th latitude).
• It's a system that designates a point or area in a concrete and easy-to-locate manner.
• It is a system used worldwide, primarily for military use.

Why Use GPS for GIS?

• It offers precise positions for points, lines, and areas.
• GIS Data Capture
• Ability to navigate to existing elements.
• Relocation of existing elements for updating and verification.
• Data maintenance.