Add another type of data layer : proportional circles

[naomap]

Is your feature request related to a problem? Please describe. The addition of cloropleth data layers triggers another idea : showing point data as proportional circles, i.e. circles whose area is proportional to the value of a numerical field.

Describe the solution you'd like

• Load point data in a layer, with a field that contains a numerical value e.g. population.
• Select "Proportional circles" as the type of layer
• Define the field used to calculate the area of each circle, and a factor to apply so that circle sizes can be adjusted
• Each point is displayed as a circle, and can be selected to show a popup.
• It may be necessary to adjust the size of circles to the zoom level, so that they do not hide each other at a low zoom level => need for another factor ?

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Example map :

[naomap]

Here is an example with Overpass Turbo : bicycle parkings where the surface is proportional to their capacity http://overpass-turbo.eu/s/1DS5

Another example with the population of cities, where a factor is required to let the circles have a sensible size : http://overpass-turbo.eu/s/1DSp. Note the sqrt() which is needed for most (all ?) types of values, so that the surface of the circle (rather than the diameter) is proportional to the value.

[yohanboniface]

May help https://github.com/balladaniel/leaflet-dataclassification