What Is A Coordinate System?

A coordinate system defines how locations are modeled on the Earth. Common examples are Latitude and Longitude, UTM zones, or Web Mercator.

A datum defines how the coordinate system is represented on the earth. For example, the earth can be flattened out to a square map or as a spherical geoid. Common examples of datums include WGS84 or NAD83.

There are two common ways of representing points on Earth's surface:

• Geographic Coordinate System (GCS) - references locations in a spherical model. These are typically in degrees. A common GCS is Latitude/Longitude which uses the WGS84 datum.
• Projected Coordinate System (PCS) - references locations on a planar, or flat surface. These systems are easier to measure discrete distances because they are in measurable units such as meters. A common PCS are UTM zones.

Most common coordinate systems have an EPSG number associated with it. This is a unique number that identifies the coordinate system: https://epsg.io/

Why Do I Need Coordinate System?

Geographical data can be represented in numerous coordinate systems (over 9k). In order to accurately display data imported into the app on top of other layers (such as web map layers), GK Field Mapper needs to know what coordinate system the data was created in.

How Do I Find The Coordinate System For My Data?

The best way is to ask the person who created your data, they will typically know the coordinate system for the data.

If the data was created in ADMS, then it will export a .prj file (for shapefiles) or a World File for images and rasters. In ADMS, shapefiles are in WGS84. Images and rasters are in UTM zones; these typcially have a prefix of '326' for the northern hemisphere and '327' for the southern hemisphere (ie, 32614 for UTM zone 14 in the N hemi). Your UTM zone will be set in Preferences in ADMS.