This week, we took a dive into georeferencing, and what possibilities this area could afford to digital humanities projects. Using the David Rumsey Map Collection, we were able to overlay a map from this collection onto a modern map. The map I overlayed can be seen in the image below, or using this link.
This map is of foreign parentage in 1870, which is the population of the US in which at least one of the parents were foreign-born. One thing that struck me about this map was how well detailed and accurate it was for its time; I never realized how accurate measurements still were from back in the day. In this way, this process gave me a deeper appreciation for the previous works we have seen of spatial DH projects, and how precise and expansive the data is for certain topics. It also helped me realize the difficulties that can arise from projections in spatial DH projects, as it was very difficult to project my map in which curvature was accounted for onto a flat map. This process broadened my understanding of how tedious and important projections are for these projects, and how extreme care must be taken to not lose accuracy in the process.
One convenient aspect from this collection is that it offers multiple formats to access my map in. It can be used in ArcGIS apps through links to Web Map Tile Service, TileJSON, and XYZ, and the map can also be overlayed and compared to other maps. Once you have a georectified map, there are many possibilities for providing more context for the map, with next steps including as adding points, lines, or polygons with labels.
As I previously alluded to, a problem with georeferencing to consider is that the accuracy of the process can be affected by things such as projection issues, or the quality of the map as well. Therefore, overlaying points onto the maps won’t be in the proper location on both due to this variability. On top of projects that would involve high levels of accuracy, this method would also not be appropriate if geographical features have significantly changed over time, because the maps would no longer have a way to align them by.
