show the diff in layer versions

[prigaux]

Hi,

After seeing github's showing changes https://github.com/blog/1772-diffable-more-customizable-maps
I wondered if it would be easy to have:

• a javascript diff library for geojson
• display the diff

So I tried for http://umap.openstreetmap.fr/fr/map/parkings-velo-paris-18e_129568#16/48.8903/2.3524,
and here is the (simple) result : http://mdb-idf.org/OSM/diff-layer.html#318917 (uses a simple umap fr proxy)

Missing:

• the diff in properties (especially "name")
• restrict to a limited number of "versions" to avoid big load on server or client (?)

Is this feature useful? Should I work on it to turn it into a pull request?

[yohanboniface]

Very nice and promising!
This is definitely useful, but I feel like it's going to be hard to implement properly: what about changes in a geometry (not adding or removing one)? Changes in metadata (editing the name for example or changing the colour) ?

[prigaux]

For geometry change, displaying the previous in red, and the new in green works quite nicely: the unchanged part is brown. See for example http://mdb-idf.org/OSM/diff-layer.html#270401, the 22/11/2016 modification.

For metadata changes, maybe a specific color could be used. For color or shape change, i don't have any good idea...

[yohanboniface]

For color or shape change, i don't have any good idea...

We may always use basic shapes, even for markers (circle), with those colours:

• green: created
• red: removed
• orange/brown: any metadata changed (even colour or shape), but no change in geo data

About the UI, I'd suggest displaying the diff on the map on mouse over in the list. Maybe adding a white semi-transparent overlay between the real map and the diff view, to have a bit of contrast and reduce colour clash.

That may be a nice MVP, and we could iterate again from there.

WDYT?

[prigaux]

Ok, i'll try. I should have some time in april.

[prigaux]

NB: I just noticed that by default umap only keeps a small number of versions (10 by default)

See LEAFLET_STORAGE_KEEP_VERSIONS used in purge_old_versions.