8 posts · 2 companies · newest first
I’ve finally crossed something off my todo list, after putting it off for years. I’ve created a new site to host the data from John Snow’s cholera map that I digitised back in 2012. Previously the data was only available from posts on this blog (specifically this original post and a follow-up), and it wasn’t […]
There has been a long gap between posts (again!), and a lot of the stuff that I’m going to talk about in this post is fairly old too. Oh well, life keeps getting in the way of blogging. Anyway, I’ve recently submitted a talk for the FOSS4G UK 2026 conference in Leeds in October, and […]
A friend was using GDAL’s ogr2ogr command to import some data to PostGIS recently, and as part of the import they were doing a reprojection of the data. They got the following error: PROJ: Cannot open https://cdn.proj.org/uk_os_OSTN15_NTv2_OSGBtoETRS.tif: schannel: the certificate or certificate chain is based on an untrusted root They’ve had various SSL errors on […]
Some data analysis I’ve done has been featured in the Financial Times today – see this article (the link may not work any more unless you have a FT subscription – sorry). The brief story is that I had terrible back pain over Christmas, and spoke to an out-of-hours GP on the phone who prescribed […]
I don’t seem to have time or energy for long posts these days, but here’s another quick post which might save you some time and frustration. Recently, I’ve been trying to import OpenStreetMap data into a PostGIS database to use with pgRouting. I wanted to import data for the whole of England – which has […]
I’ve got into a bit of a habit of writing occasional posts with links to interesting things I’ve found (probably because it’s a relatively easy blog post to write). This is another of those posts – this time, written in June 2025. So, let’s get on with some links: Why COUNT(*) can be slow in […]
I recently gave a careers talk to students at Solent University, and through that I got to know a MSc student there who had previous GIS experience and was now doing a Data Analytics and AI MSc course. Her GIS experience was mostly in the ESRI stack (ArcGIS and related tools) and she was keen […]
This post discusses the algorithm behind Personal Heatmap, one of Strava’s most acclaimed subscriber features.Product OverviewThe Personal Heatmap feature has been around in some form since 2015, but we gave it a major overhaul in 2020. For those unfamiliar, the heatmap is an aggregated view of an athlete’s GPS-enabled activities on Strava. Activity data is rendered onto a map according to path traversal frequency; the more an athlete runs on a road, the brighter — i.e. “hotter” — that road shows up on the map. The result is a beautiful color gradient displaying the intricate web of past…