# Understanding Coordinate Systems - MapInfo_Pro - 2023

## MapInfo Pro Help

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MapInfo Pro Help
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2023-09-12T16:39:16.995549

Maps at their base are a visual representation in two dimensions of a section of the three-dimensional Earth. Being able to use maps in an electronic format in many ways frees us from the constrictions of the two-dimensional map because we can use mathematical formulas to compensate for the curvature of the Earth. In this chapter, we cover the coordinate systems and projections that are standard in MapInfo Pro and provide the commands with which you can create a custom projections to meet your organization's needs. Whether you are a local government trying to establish new tax rolls or a large company trying to define your sales territory more precisely, creating a custom projection may be a solution you want to explore.

The terms "projection" and "coordinate system" are often used interchangeably, however they do not mean the same thing.

Projection - An equation or set of equations that contain mathematical parameters for a map. The exact number and nature of the parameters depends upon the type of projection. You can think of a projection as a method of reducing a map's distortion caused by the curvature of the Earth, or more precisely, a projection compensates for the shortcomings of depicting maps in two dimensions when the coordinates exist in three dimensions.

Coordinate System - When parameters of a projection are assigned specific values, they become a coordinate system. A coordinate system is a collection of parameters that describe coordinates, one of which is a projection.
Note: All coordinates are stored with respect to the northeast quadrant. The coordinates for points in the United States have a negative X, while coordinates for points in Europe (east of Greenwich) have a positive X. Coordinates for points in the Northern hemisphere have a positive Y, while coordinates for points in the Southern hemisphere have a negative Y.

You can make a map out of any globe without distorting the points on the surface by placing the globe into an imaginary cylinder.

Globe with Longitude/Latitude Projection

If you transfer the touch points from the globe surface onto the cylinder and roll out the cylinder onto graph paper, the result is a map as in the figure below. In the map that would be created from this cylinder, the Equator is 0 degrees all the way around the globe and the points on that line are completely accurate.

Longitude/Latitude Projection Map

When you add longitude and latitude lines at 15 degree increments to each side of the Equator and the Prime Meridian you create a reference grid. The lines furthest from the Prime Meridian are +180 degrees toward the right and -180 degrees to the left. This map projection is commonly called the Longitude/Latitude projection.

This is often considered the default projection. It is the most effective map for areas nearest the Equator but measurements further away tend to increase in distortion.

Because many people do not live near the Equator, other projections came into use to create more accurate local maps. Accuracy depends upon how you project the globe onto the cylinder. If you turn the cylinder so that it touches the Prime Meridian instead (or any line of longitude, 90 degrees away from the Equator) you have a Transverse Projection. The closer you are to the place the cylinder touches the globe, the more accurate the measurements are.

Globe Demonstrating the Transverse Projection

Transverse projections allow us to make maps that are more North-South line accurate, as long as you compensate for the distance from the new "Equator" which in this case is the Prime Meridian.

Figure: Transverse Mercator Projection Map

A third type of projection attempts to resolve the distortion problem in another way. Conic projections use a cone shape instead of a cylinder to create the "touch points" .

Globe with Conic Projection

This type of projection is much more accurate for large regions or countries that are wider in the East-West direction than in the North-South direction. There is much less distortion regionally because the touch points of a cone are closer to the map surface than those of a cylinder.

Brazilian Polyconic Projection Map

As you can see from the previous figure, the conic maps are best for small regional areas. The smaller-scale map has too much distortion to be useful.

A fourth type of projection, the Azimuthal projection, does not use cones or cylinders but a simple circle that goes all the way around the globe over a particular point. This projection provides a "view from space" over a particular point.

Globe with Azimuthal Projection

This type of projection is most useful when you need to work with a particular hemisphere. A hemisphere need not be North-South or East-West based. The next figure uses the North Pole as the center point for the Azimuthal Projection.

Lambert Azimuthal Projection Map

You can use more than one projection that rotates a cylinder slightly along the Equator. This style is used in the Universal Transverse Mercator (UTM) projection. UTM maps the Earth with a transverse cylinder projection to create standard "UTM Zones". By rotating the cylinder around the globe in six degree increments, the UTM assures that all spots on the Earth are within 3 degrees of the center line. (The Gauss-Kruger system is a European system akin to UTM that also uses a transverse cylinder rotated in six degree steps).

Universal Transverse Mercator Projection Map (UTM Zone 29)

Almost all projections you will use are one of these types. They are either cylindrical (regular or transverse), conic, or azimuthal projections and are customized by slightly different projection parameters. Projection parameters are options that describe how the projection is arranged.

You can further customize projections by specifying different parameters for the projection you want to use. For example, you can specify the longitude and latitude of any point on the Earth to create your own Azimuthal projection of that point. You can customize conic projections by specifying the parallel of latitude at which the cone should be tangent.