leverage "instances"

[springmeyer]

@ajashton - can you take a look at mapbox/carto#105 and comment on what this might look like to start leveraging.

@kkaefer - I assume this could help ensure the most possible efficiency in rendering in cases where you don't need to draw features in two passes (like casings)?

[ajashton]

@springmeyer and I discussed this last night - basically it's a useful/powerful feature to have in general, but there aren't situations in the FOSS4G style where we can take advantage of it. Where we have multiple symbolizers of the same type on the same layer, we need them in separate styles (the casing situation).

[kkaefer]

Yeah, I just added that because I wanted to see how I can leverage this in a style that I was working on on the weekend. There may be some situations where this is useful, but in general, you see overlapping issues which render instances unusable.