OpenHistoricalMap Cartography — Past, Present, and Future
GreenInfo Network’s cartographic journey for producing a cartographic style for OpenHistoricalMap (OHM), a modern interactive map with the added dimension of time, began several years ago with a cataloging of historical maps to be used as inspiration. There were many considerations when reviewing old maps and how they could and would be applied to a brand new style for an OHM base map.
First and foremost, we needed to consider that our new map would be applied throughout all times and geographies. This would not simply be a map styled for 1930’s America or 1700’s Japan, for example. Second, this map would be a modern interactive map that had to globally style across all zoom levels. From city streets to states to continents, a basic style would need to work for all of these scenarios. Finally, similar to OpenStreetMap, the amount and variety of types of data are massive. Our map would need to be able to coherently style many different types of data. Most historical maps have a single purpose and were designed to highlight that purpose. For that reason, historical maps also greatly limit the number of types of information displayed, where OHM is an ever-expanding landscape of data.
With the above in mind, we compiled a long list of historical maps several years ago for our team to review, which is available in this Google Doc. After some time, we settled on an aesthetic inspiration coming from the “Geographia highway map of the United States” by Alexander Gross (1950). Click the link to view this map in high resolution in David Rumsey’s Map Collection.
This map seemed like a great reference for our initial cartographic design in the first draft OHM style, given its handful of bright colors and minimal amount of basic layers. We would be able to quickly prototype a map that is immediately recognizable as a nod to vintage road maps.
Especially inspirational in the Alexander Gross map are the dusty dusky blue gray water, the warm off white land color, and the bright colors and stark contrast of the highways against the light background. These distinct colors would be the foundation of our vintage road map style, from which we would build out more subtle, complementary symbologies for land cover types, buildings, icons, and more.
Design
This first approach to an OHM style attempted to take global data at all zoom levels and symbolize it in a way that referenced 1950s road maps. Highways were given a rust red color to make them stand out, as was very typical with vintage maps of this era. We pulled the water color almost directly from the 1950 Alexander Gross map posted above. This was a great starting point to get the OHM cartography ball rolling.
While working on initial iterations, we used Mapbox Studio and their data as to test the style, since Mapbox pulls data from OpenStreetMap (OSM) which has a large amount and variety of data to work with, and an interface to quickly prototype styles.
After we knew what we wanted the style to look like, we left Mapbox and used Maputnik. Using Maputnik, we could apply the styling we created in Mapbox to OHM data (rather than Mapbox/OSM data), and we began to test the cartography across different locations, zoom levels, and times throughout history. As the style was reviewed, it became clear that the strong focus on highways and car-centric roads was not the best for all locations at all times. We toned down the saturation of water and shifted all roads to white. Roads were still highlighted by width, cases, and shield symbols and labels. This gave us more of a basic cartographic palette to work with, and allowed us to emphasize a variety of types of data, not simply transportation layers.
After some time with this new iteration of the style, some OHM users and contributors expressed how they were missing the initial draft’s variance in color that symbolized different road types, and thought colors had done a nice job of differentiating the types of roadways in the application. We listened to feedback and returned to applying colors to roads and created a few new options, but desaturated the new style compared to our original designs. We settled on this symbology, as seen in Mapbox Studio:
Here is that basic style applied to OHM data in Maputnik in the London area:
Interestingly, and maybe not surprisingly, the evolution of the OHM style started to push away from an historical map style and towards a modern interactive map style. As we bring in additional layer types to OHM, we need to be able to balance all of our layers’ symbologies more equally, and this is the focus in our current approach.
In the future, there should be opportunities to bring new influences from vintage maps, like the Woodblock and Japanese Scroll inspired styles, and we should consider more of these options moving forward!
How Data Affects Design
One of the latest challenges for the OHM base map cartography has been a lack of data, especially at a regional and global level. Below are a couple of screenshots of the most recent regional look in the production version of the OHM map style:
This map had been a nice base, but it was very limited in what it was displaying. The limited data only included land and water; and country and state boundaries and labels. To supplement our sparse data, we had some recent discussions about adding in a few global zoom levels of both hillshading and land cover / land use (LCLU). These additional layers would add an engaging and informative reference, while helping to visually resolve that issue.
To that end, we built out raster tiles that combine both hillshading and LCLU that work well at a global level, and fade to transparent at a regional level. At a global level, these relief and landcover tiles will be static (they will not change over time). At the regional level, current and future OHM land cover data will replace this static layer. The global LCLU data have been styled in a manner very similar to the current land cover data in OHM to maintain a consistency in our cartography.
To determine the best color saturation for these raster tiles, we proposed three versions: one at full color, one with a 25% white overlay on top of LCLU data, and one with a 50% white overlay on top of LCLU data.
We ultimately decided to split the difference and move forward by integrating the 25% white overlay, the middle option above. This seemed to offer just the right level of detail without being too distracting, and this layer fades nicely into the rest of the OHM data as you zoom in. You can see our latest basemap live at https://www.openhistoricalmap.org/.
If you would like to contribute to OpenHistoricalMap, please consider registering for an account!
