DOI: 10.18419/darus-3837
title: Shaded relief WebMercator 'slippy map' tiles based on NASA Shuttle Radar Topography Mission Global 1 arc second V003 topographic height data

description: This dataset contains WebMercator tiles which contain gray-scale shaded relief (hill shades), and nothing else. The tiles have a resolution of 256×256px, suitable for web mapping libraries such as Leaflet. The hill shades are generated from SRTM altitude data, which cover the land area between 60° northern and 58° southern latitude, and which lies in the public domain. Map material without political or infrastructural features can be desirable, for example, in use cases where historical data is visualized on a map. The concrete motivation for generating this map material was the Dhimmis & Muslims project (project page, home page, GitHub, DaRUS dataset), which analyzed peaceful coexistence of religious groups in the medieval Middle East. A particular goal with creating the dataset was to have map material available under a permissive license for screenshots and publications, instead of relying on proprietary mapping services such as Mapbox. Teaser image: The hillshades of Cyprus on zoom level 9. This image is hosted externally by GitHub, but is also present in the repository as teaser.png. Coverage. The dataset covers zoom level 0 (entire world in one tile) to 12 (entire world in 4096×4096 tiles). The total size of the dataset is 22,369,621 tiles. However, of those, 19,753,304 tiles (88.3%) are empty, either because the landscape there is fully flat (i.e., on water), or because they lie fully outside the latitude range covered by the SRTM altitude data. The empty tiles are not stored. Instead, a singular placeholder file is stored in the repository, alongside a list of the empty tiles. During extraction, the placeholder empty tile can be symbolically linked in the file system to all the places where it is needed. The total size of the non-empty tiles is about 103GB. Files. Besides the placeholder file and the list of empty tiles, the repository also contains a manifest file. This file lists all non-empty tiles by the ZIP file they are contained in. The tiles themselves are grouped into ZIP files by the following schema: All tiles from levels 0 to 5 are contained in one ZIP file. All tiles of level N, N≥6 are contained in a ZIP file which is named after the tile of level N-6 (block level) that contains the tile in question, named tiles______.zip. Hence, all tiles of level 6 are contained in a singular ZIP file named tiles__6__0_0_0.zip. The tiles of level 7 are split up into four group ZIP files named tiles__7__1_{0,1}_{0,1}.zip, the tiles of level 8 into 16 group ZIP files named tiles__8__2_{0..3}_{0..3}.zip, and so on. Both the manifest file and the commands to generate the distribution of tiles on ZIP files can be generated using the linked software repository. Usage. The tile ZIP files can be downloaded and extracted. By serving the extracted directory structure in a web server, a slippy map tile server can be created. The linked software repository also contains a command-line utility that generates the required shell commands to download the ZIP files, extract them, and softlink (ln -s) the empty tiles to the appropriate places. This command-line utility can also optionally read in a GeoJSON file of an area of interest. In this case, only tiles within that area are downloaded in a higher zoom level, whereas tiles completely outside the area are only downloaded to a lower zoom level; both zoom levels are also configurable. See the documentation in the repository and the command-line utility’s help (-h) output for more details.