gis

Geopoly in SQLite

I noticed this morning that one of my Datasette installations had the Geopoly SQLite extension enabled.

Serving a custom vector web map using PMTiles and maplibre-gl

Protomaps is "an open source map of the world, deployable as a single static file on cloud storage". It involves some very clever technology, rooted in the PMTiles file format which lets you create a…

Creating a minimal SpatiaLite database with Python

When writing a test for datasette-leaflet-freedraw I realized I didn't have a simple tiny recipe for creating an in-memory SpatiaLite database in Python.

Closest locations to a point

Here's a PostgreSQL SQL query that returns the closest locations to a point, based on a brute-force approach where the database calculates the distance (in miles) to every single row and then sorts by…

Downloading MapZen elevation tiles

Via Tony Hirst I found out about MapZen's elevation tiles, which encode elevation data in PNG and other formats.

GUnion to combine geometries in SpatiaLite

I was playing around with datanews/amtrak-geojson, which provides GeoJSON for Amtrak stations and track segments.

Using SQL with GDAL

Inspired by Brad Neuberg I decided to take a look at the SQL features in the GDAL family of tools. GDAL is a complex beast.

Finding duplicate records by matching name and nearby distance

I wanted to find potentially duplicate records in my data, based on having the exact same name and being geographically located within 500 meters of each other.

Constructing GeoJSON in PostgreSQL

In order to efficiently generate a GeoJSON representation of a vast number of locations, I'm currently experimenting with generating the GeoJSON directly inside a PostgreSQL SQL query using and…