English

# How To: Determine the optimal coordinate system for data in a project

## Summary

There are several factors to consider in order to determine the coordinate system for a project.

• The common coordinate system among the data. This may produce the least amount of work.
• The agencies may conform to a standard projection, in which case there may not be a choice.
• Select a coordinate system based on the type of analysis being performed, as well as the scale of the data. For example, if it is a local county versus the entire country.

## Procedure

The following scenarios model common situations requiring a combination of data from different sources. They may help to select the coordinate system that is best for a project.

In these scenarios, it is possible to substitute a projection for any of the example projections, such as UTM, State Plane, and Albers, but do not substitute a projection for the geographic coordinate system. The geographic coordinate system (DD) is not a projection. Most common scenarios involve the combination of both DD data and projected data, such as UTM, State Plane and Albers.

• Scenario 1:
All vector data is in geographic coordinates (DD).
All raster data is georeferenced to a UTM coordinate system.

Option A.
Leave the source (vector) data in geographic (DD) and the raster data georeferenced to UTM. Set the View Properties Projection to UTM.
See: How To: Set a view's map units and projection
```Note:
Since raster data is not affected by the view's projection, it overlays the vector data.```
Option B.
Project the vector data to the UTM coordinate system.

• Scenario 2.
All vector data is in Albers.
All raster data is in State Plane.
```Note:
Determine which projection provides better results for your application.```
Option A.
Georeference all raster data to the Albers coordinate system.

Option B.
Unproject the vector data to geographic coordinates, and set the view properties to State Plane.

Option C.
Reproject the vector data from Albers to State Plane.

For more information on projections, see the online ArcView Help Topics: Projections > Datums > projections, datums.