Georeferencing

Task of Lab:

The objective of the lab was to register a historical aerial photo of Baltimore City and overlay it over a present-day map.

Methodology:

1.  Downloaded an index of historical imagery of Baltimore City from 1972 from Johns Hopkins University's library website. 

2. From the index, which showed the entirety of Baltimore City, I determined where the imagery for Baltimore City's downtown area (my AOI) was and downloaded that photo from JHU's library website.  The photo I downloaded was marked as number 35 in the index.

3. Projected the map and photo to "NAD 1983 UTM Zone 18N" PCS in ArcGIS Pro.

4. Resampled the imagery to "Bilinear" and used the "Fit to Display" button on the "Georeference" ribbon to move the image onto Baltimore.

5. Transformed the image by moving, resizing, and rotating the image to roughly match the ArcGIS "Topographic" basemap, which acted as my reference map. 

6.  Added four control points, using the reference map as a guide. I made one Control Point at well-defined and easily-distinguishable spots near each of the four corners. This process fine-tuned the image to overlay over the reference image as perfectly as possible.

ArcGIS Tools Used in Analysis:

• Project

• "Georeference" on Imagery Ribbon

• "Resampling Type" on Raster Layer Ribbon

• "Fit to Display", "Move", "Scale", "Rotate" on Georeference Ribbon

• "Add Control Points" on Georeference Ribbon