In this unit, we will explore:
- rationale and advantages of analyzing historical data spatially
- tools for creating spatial representations of historical data
Tuesday, March 20
Introduction to Carto
Download these datasets:
We’ll be geocoding this data with the GPS Visualizer
What can digital mapping tell us about the past?
Ben Schmidt, ‘Data narratives and structural histories: Melville, Maury, and American whaling’, Sapping Attention (2012).
Knowles, Anne. “A Cutting-Edge Second Look at the Battle of Gettysburg.” Smithsonian Magazine, June 27, 2013. http://www.smithsonianmag.com/history/A-Cutting-Edge-Second-Look-at-the-Battle-of-Gettysburg-1-180947921
Robertson, Stephen. “Putting Harlem on the Map.” In Writing History for the Digital Age. Digital Humanities. University of Michigan Press, 2013.
Georectifying with MapWarper
This practicum has two parts:
- practice georectification of a historical map using MapWarper
- reflect on the value of georectification for historical analysis and interpretation
Part 1: Georectification
Map Warper is a tool that allows you to georectify historical maps. Georectification involves matching control points to align the map image with an existing coordinate system. After plotting corresponding points, the tool warps the historical map (using an algorithm) so that it lines up with the contemporary OpenStreetMap.
For our purposes, it will allow us to build historical map layers, which we can use to examine changes in space and place over time.
- Open Map Warper (you’ll need to create a new account if you did not do so on Tuesday)
- Upload a high-resolution map.
- Select a new map from the David Rumsey Historical Map Collection. Obviously some maps in the collection will be more suitable for georectification than others. I recommend choosing one of a city from an overhead perspective. When you find a map you want to use, click the “Export” button and choose the largest image, then download it.
- In the MapWarper window, click to “Upload Map.” Enter metadata and upload the image, and click to “Create.”
- Click the “Rectify” tab. In the side-by-side interface, you can navigate between each map using the mapping tools on the left.
- Navigation: Click the white triangles to move up/down/left/right.
- Zoom: Click the plus or negative signs to zoom in or out one step. Move the blue slider button to move multiple steps at once. (Note: you may also use your mouse/trackpad to pan and zoom).
- Locate shared points on each map. Use the controls at the top right to add and modify Control Points on each map. (Note: You should add at least three points to rectify. Focus on locating points across the map- not in one single area)
- Add Control Point: Click the small pencil button to add points. Click again on the map to place the marker.
- Move Control Point: Click the arrow button to edit control point positions. Click again on the point to move it. Click to place the point in the new position.
- Move Around Map: Click the small hand button to easily move around the viewer. Click, hold, and drag to slide the map around. Release to place it.
- Below the map images, click “Control Points” to see a list of points.
- After you have added points, click “Warp Image.” Click the “Preview Map” tab. A “Transparency” slider will allow you to compare the two maps in your window. (Note: you can return to the “Rectify” tab to add/edit points to improve your results.)