I'm a civil engineer. What we often call GPS is officially "geographic coordinates" or "latitude and longitude". GPS is more correctly the satellite system that allows real-time, map-free positioning. GIS (geographic information system) is a database that has coordinates on everything.
Two ways to get the geographic coordinates (lat and lon) for an event are: 1. Manually determine where the event fits on a modern map or aerial photo (Google Maps) and pick off the coordinates. 2. Lookup the location identifiers (zip code, address, point of interest) in a geo-coded database, or GIS. Latitude and longitude are by definition stable across time with 0 degrees longitude running through Greenwich, England. The difference between the two canonical precise datums, NAD27 and NAD83/WGS 84 is insignificant for genealogy work. BOTTOM LINE: I don't know if old systems like the censuses and old town names have been geocoded by date into GISes. But putting latitude and longitude into genealogical event data would be a wise move. Tom
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