Simon Willison’s Weblog

GPSJam (via) John Wiseman’s “Daily maps of GPS interference” —a beautiful interactive globe (powered by Mapbox GL) which you can use to see points of heaviest GPS interference over a 24 hour period, using data collected from commercial airline radios by ADS-B Exchange. “From what I can tell the most common reason for aircraft GPS systems to have degraded accuracy is jamming by military systems. At least, the vast majority of aircraft that I see with bad GPS accuracy are flying near conflict zones where GPS jamming is known to occur.” # 30th July 2022, 7:51 pm

Datasette for geospatial analysis (via) I added a new page to the Datasette website describing how Datasette can be used for geospatial analysis, pulling together several of the relevant plugins and tools from the Datasette ecosystem. # 13th April 2022, 12:48 am

geoBoundaries. This looks useful: “The world’s largest open, free and research-ready database of political administrative boundaries.” Founded by the geoLab at William & Mary university, and released under a Creative Commons Attribution license that includes a requirement for a citation. File formats offered include shapefiles, GeoJSON and TopoJSON. # 24th March 2022, 2:03 pm

country-coder (via) Given a latitude and longitude, how can you tell what country that point sits within? One way is to do a point-in-polygon lookup against a set of country polygons, but this can be tricky: some countries such as New Zealand have extremely complex outlines, even though for this use-case you don’t need the exact shape of the coastline. country-coder solves this with a custom designed 595KB GeoJSON file with detailed land borders but loosely defined ocean borders. It also comes with a wrapper JavaScript library that provides an API for resolving points, plus useful properties on each country with details like telepohen calling codes and emoji flags. # 18th April 2021, 7:37 pm

Spatialite Speed Test. Part of an excellent series of posts about SpatiaLite from 2012—here John C. Zastrow reports on running polygon intersection queries against a 1.9GB database file in 40 seconds without an index and 0.186 seconds using the SpatialIndex virtual table mechanism. # 4th April 2021, 4:28 pm

California Protected Areas Database in Datasette (via) I built this yesterday: it’s a Datasette interface on top of the CPAD 2020 GIS database of protected areas in California maintained by GreenInfo Network. This was a useful excuse to build a GitHub Actions flow that builds a SpatiaLite database using my shapefile-to-sqlite tool, and I fixed a few bugs in my datasette-leaflet-geojson plugin as well. # 21st August 2020, 11:15 pm

geojson-to-sqlite (via) I just put out the first release of geojson-to-sqlite—a CLI tool that can convert GeoJSON files (consisting of a Feature or a set of features in a FeatureCollection) into a table in a SQLite database. If you use the --spatialite option it will initalize the table with SpatiaLite and store the geometries in a spacially indexed geometry field—without that option it stores them as GeoJSON. # 31st January 2020, 6:40 am

kepler.gl. Uber built this open source geospatial analysis tool for large-scale data sets, and they offer it as a free hosted online tool—just click Get Started on the site. I uploaded two CSV files with 30,000+ latitude/longitude points in them just now and used Kepler to render them as images. # 25th October 2019, 4:16 am

Thematic map—GIS Wiki. This is a really useful wiki full of GIS information, and the coverage of different types of thematic maps is particularly thorough. # 21st October 2019, 2:25 am

Los Angeles Weedmaps analysis (via) Ben Welsh at the LA Times published this Jupyter notebook showing the full working behind a story they published about LA’s black market weed dispensaries. I picked up several useful tricks from it—including how to load points into a geopandas GeoDataFrame (in epsg:4326 aka WGS 84) and how to then join that against the LA Times neighborhoods GeoJSON boundaries file. # 30th May 2019, 4:35 am

VirtualKNN for SpatiaLite. This looks amazing: a special virtual table shipped as part of SpatiaLite 4.4.0 which implements a fast, R-Tree backed mechanism for finding the X nearest points against a geospatial database table. There’s just one catch: it’s only available in 4.4.0, but the most recent “stable” release of SpatiaLite is 4.3.0a from September 2015 so the version you get if you install from apt-get or homebrew doesn’t yet have this functionality. I’d love to figure out a neat way to package and distribute this along with Datasette. I’d also like to figure out a clean way to ship a more recent version of SQLite than the one that is currently packaged with Python 3 (3.16.2, where the latest SQLite release is 3.23.1). # 21st May 2018, 9:23 pm

Nicaraguan Address System (via) “Instead of street names or numbers Nicaraguans use reference points from where they start describing a certain address. [...] There are instances, however, in which the reference points do not exist anymore!” # 21st January 2018, 4:32 pm

Generating polygon representing a rough 100km circle around latitude/longitude point using Python. A question I posted to the GIS Stack Exchange—I found my own answer using a Python library called geog, then someone else posted a better solution using pyproj. # 17th January 2018, 8:57 pm

simonepri/geo-maps. Neat project which publishes GeoJSON maps of the world automatically derived from OpenStreetMap. Three variants are available: country political maritime boundaries, country political coastline boundaries and a general outline of the world’s land territories. # 21st November 2017, 4:06 pm

Interactive Database of the World’s River Basins (via) “This database provides the first-ever compilation of the world’s river basins developed specifically for corporate disclosure. It features a comprehensive list of river basins worldwide, including their names, boundaries, and other helpful information.” # 10th November 2017, 3:07 pm

Fast GeoSpatial Analysis in Python. Some clever advanced performance tricks with Cython and Dask, but it also introduced me to GeoPandas. # 29th October 2017, 4:47 pm

Geospatial Indexing in MongoDB (via) New in version 1.3.3. Handles “order by distance from” queries using a geohash approach under the hood, automatically searching nearby grid squares until the correct number of results have been gathered. Bounding box search is planned for a future release. # 2nd March 2010, 8:12 pm

On walking into a disaster zone. Schuyler Erle: “The World Bank was looking for technical GIS professionals, ideally French-speaking, to go and advise the government [...] I can sort of speak French. Sure, why not?” # 10th February 2010, 3:45 pm

The making of the NYT’s Netflix graphic. A database dump from Netflix, some clever hackery in ArcView GIS, hpricot to scrape Metacritic and a lot of careful thought about the UI for navigating the data. # 25th January 2010, 1:11 pm

GeoDjango and the UK postcode database. Excellent introduction to GeoDjango using the recently leaked UK postcode database. Obviously, you should only follow the steps in this tutorial using the officially licensed database, available for a mere £1,700. # 30th September 2009, 2:25 pm

openstreetmap genuine advantage. The OpenStreetMap data model (points, ways and relations, all allowing arbitrary key/value tags) is a real thing of beauty—simple to understand but almost infinitely extensible. Mike Migurski’s latest project adds PGP signing to OpenStreetMap, allowing organisations (such as local government) to add a signature to a way (a sequence of points) and a subset of its tags, then write that signature in to a new tag on the object. # 29th September 2009, 9:49 am