Module 3 - Introduction to Projections

In this lab titled “Introduction to Projections”, we covered different map projections and how these projections will cause various types of distortion.

First, we downloaded Florida County Boundaries shape file from FGDL.org, extracted the data and inserted it in a new map. From the layer properties, we noted that the layer is projected to Albers Conical Equal Area. Using the Project tool under Projections and Transformations in the toolbox, we reprojected Florida boundaries layer to a new projection, NAD 1983 UTM Zone 16N, and renamed the new output layer utm16. Following the same process, we reprojected the original layer to NAD 1983 HARN State Plane North with a new output name, StatePlaneN. We copied and pasted the new projected layers, each in a new map, and renamed the maps appropriately. After creating the new maps, we compared the different projections visually and noticed Albers and State Plane map projections were very similar, while the UTM projection was noticeably tilted more counterclockwise.

The next step was to compare the three different projections quantitatively. To do that, we used Calculate Geometry Attribute tool to calculate areas in US miles for all Florida counties in the three different projected layers. Following this, using select by attribute, we selected 4 counties (Alachua, Escambia, Miami-Dade, and Polk counties) and created a new layer from the selected features. This layer is a temporary layer to show only the four counties of study. Repeating the same process to create a new layers for the same counties for the other two maps, UTM16 and State Plane N.

Finally, we created a layout and inserted the three different projected maps. We then exported the data for the three different projected layers to an Excel sheet and created a new table showing areas in square miles for the four different projected counties, Following that, we inserted the table in the layout. We finished by adding all essential map element (Title, North arrow, Scale bar, legend, etc...) to the layout and exporting it to PNG file.

We also tested a raster projection by adding a .jpg file to an Albers map, but the image appeared in the wrong location. However, when we inserted the same image into a State Plane N map, it displayed correctly. This happens because the image is using the State Plane coordinate system. Now that we know the image's coordinate system, we can reproject it to the correct system for the Albers map.

Results and Conclusions

A map projection is a systematic transformation of the 3-dimensional Earth into a 2-dimensional flat map (Iliffe, 2008; Garnett, 2009). This transformation will create some distortion. The four spatial properties subjected to distortion are shape, area, distance, and direction. In this lab, we demonstrated how various projections of the same feature layer can distort characteristics of the feature. We noticed that UTM 16 projection differs the most in Alachua, Miami-Dade, and Polk counties. A GIS professional should always select the appropriate map projection for the project. For example, Florida Geographic Data Library (FGDL) map Projection is a custom map projection based on the Albers Conic Equal-area map projection, which is the best for the entire state of Florida map projection.