This photo states that it was taken in 1894 at the NW corner of 15th and Pennsylvania Ave.
In 1895 Pennsylvania Ave. ran along the railroad tracks that are now between Hamilton and Callowhill.
That intersection no longer exists, as Pennsylvania Ave. now ends around the intersection of 22nd and Hamilton.
We have the photo geocoded as 15th and Hamilton as that is the current address for the same location.
Most people have experienced typing an address, intersection, or other location description into an online application which then converts it into coordinates that can be used to pinpoint the location on a map. This is the part of the process called “geocoding”.
Creating geocoding software is almost never a simple process. The more variables involved in the software, the more complex the geocoding process becomes. One of these variables is time and the change of place names over time. In our spare time we have been developing an application called a Historic Geocoder, through which we aim to address the difficulties of geocoding historic pieces of information with a ‘current’ set of location data.
A good example of an Azavea application that uses geocoding is PhillyHistory.org, a publicly accessible site run by the City of Philadelphia Department of Records and City Archives. The site is a searchable collection of some of the approximately 2 million historic photos stored in the City Archives. A unique feature of the site is that a visitor can search by a current address and find pictures near that address.
Over the years the City photographers have documented the location of each photograph by using addresses. However, the catch is that sometimes street names change. When this happens, a historic photograph with a location description that has since changed is geocoded to the wrong coordinate location or cannot be geocoded at all.
Our Historic Geocoder research project consists of three parts: a) a record of street name changes; b) a database of street segment changes; and c) software to enable time-based geocoding.
By recording not only where current streets are and what they are named, but also where streets were in the past and what they used to be called, the Historic Geocoder will provide us with the ability to geocode based on both space and time. Instead of only entering a location, a user will be able to enter a location and a date and the system then locates where the historic address was during that time period on a current map.
Historic photos are not the only records with potential historic address problems. Surveys, censuses, and legal records all use addresses to describe locations. Being able to geocode these locations with relation to time is a very important first step towards the analysis of these data. Through our R&D work on a Historic Geocoder, we hope to make it possible to more accurately assign locations for historic data.
