Civil Engineering Transportation GIS Workshop
- Geographic coordinate system: locations defined on earth using a three-dimensional spherical surface (sphere or spheroid)
- A point is referenced by its longitude and latitude values.
- Projected coordinate system: defined on a flat, two-dimensional surface.
- Has constant lengths, angles, and areas across the two dimensions.
- Always based on a geographic coordinate system.
Source & Additional Information - ESRI Guide: What are map projections?
Esri Training: Basics of Map Projections
- The same location on the ground will have different coordinate values in different geographic coordinate systems.
- Displaying data in a projected coordinate system can exaggerate the differences which can be from a few centimeters to hundreds of meters.
- If you are using datasets that are based on different geographic coordinate systems, you will need to set a geographic transformation.
Source & Additional Information - ESRI Guide: Choosing an appropriate transformation
Issue: Datasets do not line up when added to ArcMap.
- If there is no coordinate system associated with the data, or
- If the coordinate system definition is incorrect, or
- If the proper geographic (datum) transformation is not specified,
the data will not line up properly with other data displayed in the map document.
Additional Information & Source - Technical Article: Problem: Datasets do not line up when added to ArcMap
- Last Updated: Feb 28, 2018 12:56 PM
- URL: https://library.ucalgary.ca/encigisworkshop
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