Our library is undertaking a project to map historical data regarding 18th and 19th century British and American printers and publishers. One of the problems that we have encountered is the different granularity of location data. For example, one publisher may list a street number, street name, and city whereas another publisher may only mention a street name or even only the city. In such cases, we are wondering the best way to georeference the location and present this approximate data. Does the spatial humanities community have rules or conventions for dealing with these cases? Also, what are the most effective ways for visualizing “approximate vs precise” geospatial data on the same map? Any suggestions or resources that you can offer would be greatly appreciated!
This is an interesting challenge. Here's my suggestion.
Define each uncertain location as a polygon defining an area that you are "reasonably certain" contains the actual location. Such polygons could cover streets, cities, city blocks, a single address, etc.. For visualization the symbology could scale the polygons' fill transparency inversely with the amount of area they cover, i.e. large (imprecise) polygons would be rather feint, whereas smaller (more precise) polygons would appear more distinct. I think this would keep the large polygons from visually dominating.
I'm not sure how this would work out in a case where multiple polygons cover the same area, e.g. an entire city. One solution to this would be to offset such polygons from each other a bit, as points in a box plot can be "jiggled" apart. Precisely known locations could be identified with opaque points on top of the polygon layer(s) and displayed at a size that fits the location or map scale.