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ArcGIS Pro
Projecting Geographic Data
Introduction
When flattening the Earth’s curved surface onto a flat map, there is unavoidable distortion. When producing different map projections, there are identical points with different X and Y coordinate values, which correspond to East and North values. It is very important to keep these map projections separate in analysis. A way of ensuring this is by re-projecting our data layers.
In this lab, I worked with a dataset to work with coordinates and on-the-fly projection, and worked with different coordinate and projection systems. In addition, I learned how to use GIS software like ArcGIS Pro to create maps that included locator maps, insets, and critical information to be able to read the product.
Software Used
Observing How Distance May Change with a Map Projection
To understand how distance changes with a map projection, I first measured the distance between two cities, Los Angeles and New York, on a normal topographic map. The distance was approximately 2,440 miles. Then, I activated the Mercator map provided and re-measured the distance, which was approximately 3,127 miles. This revealed the unavoidable distortion caused when stretching measurements from the Earth’s curved surface to a flat map.
Coordinates and On-the-Fly Projection
Next, I was introduced to a temporary projection. With a map, the coordinate system is often specified; however, in ArcGIS Pro, the system can automatically establish one when the data first loads. I learned how to view and set the coordinate system for a map to which every layer is temporarily projected. In addition, I explored different coordinate systems, such as the NAD83 (2011) Contiguous USA, the GCS WGS84, and more. In each geographic coordinate system, the shape of the map changed, which implied that the projection of the data was not changing, but rather, I was telling ArcGIS Pro to project on the fly to a new system.
Deliverables
Figure 1. Page 16 Minnesota Counties
Figure 2. Page 27 3 Minnesota Projections
Summary
Map projections are incredibly important as they transform Earth’s curved 3D surface onto a 2D map. This allows for accurate spatial analysis, data display, and accuracy. With this process, distortions are imminent and can compromise the map’s usefulness. This lab introduced ways to fix and account for unavoidable distortion when working with projections.
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