Building the Salem Witchcraft GIS


Digitizing the Upham Map

C. Identifying Data to Record from Upham's Map

Digitizing Upham's map involves several different steps:

  1. Test digitizing : For demonstration and experimentation purposes, immediately digitize the points of Upham's map.
  2. Establish control points : Simultaneously research information about existing sites depicted on Upham's map, so that the data created from this map could be matched to other contemporary data about Salem and Essex County, Massachusetts.
  3. Registration of the map : Use control points to register, or fix, the real world location of Uphams points, and assigning geographic coordinates to the image.
  4. Digitize georeferenced points : From the registered image, digitize points and harvest geographic coordinates.
  5. Adjust locations : Compare Upham's map to known contemporary data and correct his locational data as necessary.
  6. Build and link attribute database : Link the geographic data to an attribute database about the participants in the trials to create demographic mapping.
  7. Merge data from Upham with data created from other sources : Georeferenced data will match with data created from the Pereley/Freeman and Andover Historical Society maps.

This process is slightly backward from what might usually be done: that is, we might normally have first researched existing sites to obtain a series of known "control points" that could be used to anchor the Upham map as we digitized. However, we recognized that this would take time and effort, and we felt that it would be useful to have a point coverage of Salem available to experiment with, even if it were not "geographically aware," or referenced to a real-world coordinate system.