Notes on the history of the map tile
Web map tiles—the storing of geospatial data at different zoom levels in x/y/z indexed squares of raster (and later, vector) data for efficient storage and transmission of digital maps—are, despite their seeming simplicity, I think one of the most significant developments in geospatial software history. Tiling transformed the user experience of digital maps from one of tedious clicks-and-reloads to one of fluid, dynamic exploration. It made digital maps feel spatial, an interface that one literally moved through and across rather than a static image. This interactivity changed what everyday people expected of digital maps and likely were the gateway for a lot of people even getting interested in maps and geographic knowledge. (I know this was my experience!)
Despite their importance, I’ve found it weirdly hard to identify the genesis of digital map tiles. In general, credit tends to be given to Google Maps (or to Where2 Technologies, the 4-person company they acquired that became Google Maps) because they 1) were the first to implement raster tiles in a high-profile way and 2) they filed a patent for the method. But I haven’t found any interviews with or writing by any of the other original Where2 founders that actually gets into how they’d landed on the tile method.
This is probably not because the Where2 founders are humble dudes but because the concept of tiling map data was already out in the world, tried out by lots of people in different contexts.
Pre-web GIS tiling: there from the very beginning
The idea of breaking up a map into squares or rectangles isn’t a huge theoretical leap when looking at a print map with graticule lines that effectively do the same thing, and the idea of individual sheets of maps adding up to a larger world map was central to the ill-fated International Map of the World project chronicled by William Rankin in After The Map. So it’s maybe not surprising that methods for breaking up map data into “tiles” appeared in what’s maybe not the first “actual” Geographic Information System, but certainly the first project to call itself that.
In an essay about the Canada Geographic Information System (CGIS), developed by Roger Tomlinson in collaboration with IBM for the Canadian government, Tomlinson mentioned its use of a tile-based data structure (emphasis mine):
A key role was played by Guy Morton, who designed the data structure now known as the Morton Matrix, which was the underlying strength of the system. It involved creating “frames” to hold data in the largest units that could be conveniently processed by the computers available at the time. This concept was the origin of “tiling” employed in most modern GIS.
The Morton Matrix was known in France as the Lebesgue curve, after a French mathematician who first explored the concept in 1904, and is better known today as the z-order curve. Morton wrote up the method in a paper about the CGIS that currently can be found behind an expired SSL certificate on an old IBM server (I’m posting the PDF here for the sake of convenience). The logic of this data structure was partly driven by the material conditions of data storage, as Tomlinson explained:
The arrangement of the unit frames was crucial to operating efficiency of the system. Random access discs were not available in the early stages of system design, and searching a magnetic tape for data was a time-consuming sequential process. To overcome this constraint on the system’s efficiency, it was desirable that frames close together in the sequence should refer to locations close together on Earth’s surface and, similarly, that records from close locations on Earth should have the least possible separation in a sequential file.
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