Make OSMWidget zoom level configurable

[Danilo Bargen]

The OSMWidget has a default zoom level of 12 (as seen in django/contrib/gis/static/gis/js/OLMapWidget.js on line 55).

default_zoom: 12,

That zoom level is not only used as default zoom level, but also as max zoom level for fitting the map to data:

this.map.getView().fit(extent, this.map.getSize(), {maxZoom: this.options.default_zoom});

This causes maps to be zoomed out considerably even when showing a pretty small polygon with a few meters in diameter. That makes fitting the zoom level to the data pretty useless.

Unfortunately this value is not configurable, in contrast to default_lat and default_lon. Therefore as a first, non-controversial change I'd suggest to make this value configurable in the OSMWidget. I'll provide a pull request for that shortly.

Some further comments:

• The default zoom level should probably be decoupled from map zoom fitting.
• The default zoom level is different from the one used in admin, where it's 4: https://code.djangoproject.com/ticket/26774

[Danilo Bargen]

​PR

[Tim Graham <timograham@…>]

In a7975260:

Fixed #28195 -- Added OSMWidget.default_zoom attribute.