On Tuesday, I georectified Rand McNally Transcontinental mileage chart of the United States (Figure 1) using David Rumsey Map Collection. The process of georectifying a historic map helped me better understand other spatial DH projects. Previously, I wasn’t sure how poeple create a digital map based on history documents and drawings. I was also confused when I openned most of the projects, the name of the location appeared in Chinese. I thought those projects were using some external mapping technology (that supports different languages), and this conjecture turned out to be true: many projects just overlay data on an external map library.
Possbilities
Multiple formats of the map, including GeoTIFF, JSON, and XYZ tiles, are available for access in this tool. The map could be exported and used in other platforms though those formats. Georectified maps exhibit the geographical relations among data points in an intuitive way. I could imagine multiple layers of maps are overlayed and comparing the relationship of different variables. Moreover, if we have a series of historical records, we might be able to project them onto the map and see how event shift along with time. Once we have a georectified map, I could imagine creating interactive projects based on the maps and sharing them with the general public.
Problems
One problem with georeferencing is that old maps aren’t always accurate. Thus, when georectifying them, there could be distortion and mismatch in locations. Another problem is that a visualization usually requires a fair amount of data, and most data has to be quantified (e.g. how many population are there) or digitalized (e.g. what are locations of canals). It is less appropriate for disciplines with non-geographical data. For example, research questions like the use of words by a specific author or the shift in painting styles are hard to be answered use the GIS method.
2 thoughts on “Georeference Reflection”
Comments are closed.
I find the possibilities for overlapping layers of data using this method really exciting. I agree that looking at a georectified map makes the possibilities of creating interactive web mapping projects much more real and I could really see how it works. I was also very confused about how mapping projects were truly created prior to this project.
I agree strongly with the possible fallacies of old maps and potential errors in georectification. It is definitely a problem working with data of a smaller scale or corrupted data in such that it is more prone to errors. As far as I think, if the historical maps contain latitude and longitude values for certain points though, we could probably make it easier to be overlapped to the other map.