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Introducing offline_folium

Another new-ish package that I’ve never got around to writing about on my blog is offline_folium. It has a somewhat niche use-case, but it seems like a few people have found it useful.

In brief, it allows you to use the folium package for creating interactive maps from Python, but without an internet connection. Folium is built on top of the Leaflet web mapping library – and it loads all the relevant JS and CSS files directly from CDNs. This means that if you try and use folium without an internet connection it just doesn’t work. Offline_folium works around this by downloading the files when you do have an internet connection, and then re-writing the links to the files to point to the offline versions.

I originally created this package when doing freelance work on a project for the UK Navy – they wanted to have interactive maps on an air-gapped computer, so I built a system that would allow this (in this case, the JS/CSS file download step was run as part of building the ‘app’ we produced). I should note at this point that without an internet connection the default OpenStreetMap background mapping will not work. In some situations that would be a significant problem – but we were using other background mapping, coastline vector files and so on, so it wasn’t a problem for us.

So, how do you use this package?

First, install it using pip install offline_folium. Then make sure you have an internet connection and run python -m offline_folium – this will download the JS/CSS files and store them in a sensible place (chosen automatically). Now you’re all set up.

Once you have no internet connection and want to use folium, you must import it in a slightly different way – first import offline from offline_folium, and then import folium, like this:

from offline_folium import offline
import folium

Now you can use folium as usual, for example by creating a simple map object:

m = folium.Map()

So, that’s pretty-much it. People are actively submitting pull requests at the moment, so hopefully the functionality will expand to work with various folium plugins too.

For more information (or to submit a PR yourself), see the Github repo.

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This post originally appeared on Robin's Blog.

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Categorised as: Academic, GIS, My Software, Previously Unpublicised Code, Python