I first learned the word “metadata” in 2008, when I was first hired at what is now known as the Map & Data Library at the University of Toronto as a research assistant on the Don Valley Historical Mapping Project. After mastering the basics of georeferencing and digitizing in ArcGIS, I dutifully warped approximately one hundred historic maps of Toronto into place on the digital street grid, traced the course of the Don River and the wharves of the changing waterfront, and labelled six hundred points with the names and addresses of business and factories operating in the late 19th and early 20th centuries. As the project wrapped up one year after I started, we published several thematic digital map layers in two different formats, allowing viewers to overlay the environmental and industrial history of the lower Don Valley on the contemporary city in ArcGIS or Google Earth. However, how and why should a reader of these maps trust the data in them, considering a) very few of the locations mapped still exist in the present, and b) there is sometimes a mismatch between the location of features mapped at different times? (For a greater explanation and visualization of this problem, please see pages 50-52 of Marcel Fortin and Jennifer Bonnell’s chapter “Reinventing the Map Library”, part of their excellent edited volume Historical GIS Research in Canada, available as a free ebook from the University of Calgary Press.)
As it was up to me to communicate the contingencies of this research process and the individual sources themselves to users of these geospatial datasets, I learned that the answer to both of these questions lay in the metadata that would accompany them. Through the metadata creation tool included as part of our GeoNetwork installation, I created ISO 19139-compliant metadata for all layers we created containing information about the rationale of the dataset within the broader scope of the project, credits for those who worked on it, bibliographic details about the accompanying sources, and explanations about what given database entries mean in a historical context. As we worked from cartographic and textual sources to assemble our datasets (some of which conflicted with each other), we could not state that a business definitively existed at certain points in time, only that it appeared on the map at certain points in time. These important definitions and their implications were contained in the metadata.
Since the project wrapped up in 2009, I have worked on several more historical GIS projects at UofT, including a complete mapping of the Los Angeles streetcar network in the 1920s and a growing collection of historical hydrography datasets showing the changing shoreline and lost rivers of Toronto. This first project taught me the importance of geospatial metadata in the context of using GIS for historical research. In my next post, I will discuss how frustrating it can be when working in a GIS without metadata.
Bonnell, Jennifer, and Marcel Fortin. 2014. Historical GIS Research in Canada. Calgary: University of Calgary Press.