How can I add a legend to a folium map?

[ElmWer]

The position of the legend should be in "window coordinates", similar to mpl.legend(loc='upper left')

[ocefpaf]

We only have a built-in legend for the choropleth but that logic could be re-factored to be more generic. See the fullscreen.py plugin as an example, since legends will be using Leaflet's L.control, in case you want to send a PR.

[easherma]

Legend creation would be great!

[BibMartin]

According to this page's latest example, you just need to:

import branca.colormap as cm
colormap = cm.linear.Set1.scale(0, 35).to_step(10)
colormap.caption = 'A colormap caption'
m.add_child(colormap)

But :

• the position is fixed to 'topright'
• there is no white background color
• the final div (colormap_24798749.legend._container) has to be of class leaflet-bar so that we get the nice shadow around it.

I'll try to PR this in branca, but it would be interting if someone create a folium plugin that enable to put a control in a map with any kind of html.

[BibMartin]

BTW: we could have a method in folium.Map taht helps the creation of the legend.

[ocefpaf]

BTW we are using a using a language for colorbar and legend as if they are the same same. Even though the implementation is/could be similar we need to make a distinction. Colorbars are already supported and easy to create. The limitations @BibMartin mentioned above are not pressing issues (but any PR improving that is welcomed.)

Legends can be complex, like those with a callback that when clicked navigate to a map position or highlight a region, or they can be simple static images. I believe that the former is quite hard to implement in a generic way that folium can handle, but the latter is supported in latest master thanks to #537

#537 could use L.control to control the position relatively to the map BTW.

[araichev]

One could take inspiration from Leaflet for R.
Here's their addLegend function.

[prhbrt]

A workaround is to inject CSS-style in the FeatureGroup-name

The name is (rawly) injected in a {" .... " : value} json-object, so all double quotes need to be escaped for javascript, hence the \\.

https://github.com/python-visualization/folium/blob/master/folium/map.py#L105

import folium

m = folium.Map((51, 6), tiles='stamentoner', zoom_start=7)
    
group0 = folium.FeatureGroup(name='<span style=\\"color: red;\\">red circles</span>')
for lat, lng in zip(range(500, 520), range(50,70)):
    folium.CircleMarker((lat/10, lng/10), color='red', radius=2).add_to(group0)
group0.add_to(m)

group1 = folium.FeatureGroup(name='<span style=\\"color: blue;\\">blue circles</span>')
for lat, lng in zip(range(500,520), range(70,50,-1)):
    folium.CircleMarker((lat/10, lng/10), color='blue', radius=2).add_to(group1)
group1.add_to(m)

folium.map.LayerControl('topright', collapsed=False).add_to(m)

m

[ColinTalbert]

I had a similar need but for a categorical legend.

Here's my solution that I'd like to share ( I really like that it's dragable as well.):
http://nbviewer.jupyter.org/gist/talbertc-usgs/18f8901fc98f109f2b71156cf3ac81cd

I'd love to see something like this get added to folium, but I understand that there are lots of moving parts. If there's any way I can help on a PR I'd be happy to, but I haven't contributed to folium before.

-- Colin

[davidolmo]

@talbertc-usgs solution is very nice. Thanks for sharing. The only problem is that it takes a lot to load (is it downloading any very big css?)

[OneAdder]

I had a similar need but for a categorical legend.

Here's my solution that I'd like to share ( I really like that it's dragable as well.):
http://nbviewer.jupyter.org/gist/talbertc-usgs/18f8901fc98f109f2b71156cf3ac81cd

I'd love to see something like this get added to folium, but I understand that there are lots of moving parts. If there's any way I can help on a PR I'd be happy to, but I haven't contributed to folium before.

-- Colin

Hi, your template looks very handsome. Would you mind if I implement it into a small project I'm working on?

[alex-gottlieb]

@talbertc-usgs Thanks for that solution! Do you know if there's a way to bind the legend element to a map layer so it dis/appears when the layer is selected in LayerControl?