Posted on December 30, 2022 (Updated on July 19, 2025)

Extract data from a WMS with database

Hiking & Activities

Getting Data Out of a WMS and Into Your Database: A Human’s Guide

Okay, so you’ve got a Web Map Service (WMS) – think of it as a way to grab a picture of a map over the internet. It’s like asking a GIS server to send you a screenshot of its map database. But here’s the thing: WMS wasn’t really designed to give you the data behind the map, just the pretty picture. That can be a bit of a headache when you actually need that data in your own database!

WMS is all about requests and responses. Your computer sends a request, specifying things like the area you’re interested in, which layers you want to see (roads, rivers, buildings, you name it), and how you want the map to look. The WMS server then crunches the numbers, pulls the data from its GIS database, and spits out a map image – usually a PNG, JPEG, or GIF. Simple, right?

But here’s the rub: you’re getting a picture of the data, not the data itself. It’s like trying to extract the ingredients from a finished cake! So, how do you actually get your hands on the good stuff?

Well, it’s not always easy, but there are a few tricks up our sleeves. Let’s explore some ways to wrestle that data out of a WMS and into a format you can actually use.

  • The “GetFeatureInfo” Poking Method: WMS has this little-known feature called “GetFeatureInfo.” It’s kind of like poking a pixel on the map and asking, “Hey, what’s here?” The server will then (hopefully) tell you about the features at that spot. You can specify the output format using the INFO_FORMAT parameter, with options like text/plain or text/xml.

    Now, in theory, you could repeatedly poke the map, pixel by pixel, and try to piece together the whole dataset. But trust me, that’s about as fun as watching paint dry. It’s slow, tedious, and often impractical, especially if you don’t know exactly where to poke.

  • WFS: The Holy Grail: If you’re lucky, the WMS provider also offers a Web Feature Service (WFS). Think of WFS as WMS’s cooler, more data-friendly cousin. Instead of just giving you a picture, WFS actually gives you the vector data – the points, lines, and polygons that make up the map, along with all their attributes. Jackpot!

    If you find a WFS endpoint for the same data as your WMS, grab it! Tools like ogr2ogr can then slurp up all that sweet vector data and save it into a format you can load into your database, like GeoJSON.

  • GDAL/OGR: Your Geospatial Swiss Army Knife: GDAL (Geospatial Data Abstraction Library) is a ridiculously powerful open-source library for all things geospatial. OGR, which is part of GDAL, specializes in vector data wrangling. I’ve personally used it on countless projects.

    With ogr2ogr, you can convert data between formats, reproject it, and even pull data directly from web services like WFS and WMS. It’s like the Swiss Army knife of the GIS world.

    Want to save a WFS query as a GeoJSON file? ogr2ogr has you covered. Need to convert a Shapefile to PostGIS? ogr2ogr to the rescue!

  • QGIS: The Visual Approach: QGIS is a fantastic, free, and open-source GIS software package. While it’s primarily used for displaying geospatial data, it also has some handy tools for extracting information from WMS layers.

    For example, the “Identify Features” tool lets you click on a feature in the map and see its attributes. It’s not ideal for extracting large datasets, but it’s great for quickly grabbing information about specific features.

  • Raster to Vector: The Last Resort: Okay, so you’re stuck with only a WMS, and you really need the data. As a last resort, you could try to extract vector data from the raster image. This involves converting the map to a raster, then using image processing techniques to identify and extract features like roads, buildings, or contour lines.

    I’m not going to lie: this is a pain. It’s complex, time-consuming, and often requires a lot of manual cleanup. But if you’re desperate, it’s an option.

    • Let’s Get Practical: Using GDAL/OGR to Grab Some Data

    Alright, enough theory. Let’s walk through a real-world example of extracting data from a WMS using GDAL and ogr2ogr.

  • Get GDAL Installed: First things first, you need to download and install GDAL. Make sure you add it to your system’s PATH so you can run the commands from the command line. Seriously, don’t skip this step.

  • Find That WMS URL: You’ll need the URL of the WMS service. It usually ends with something like “?service=WMS&request=GetCapabilities”.

  • See What’s Available: Use gdalinfo to list the layers in the WMS:

    bash

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