Islet names rendering

[sommerluk]

This fixes #159 and #988 using the system proposed in #941.

Is rendering from zoom level >=7 okay (performance)? Would probably be low enough to solve #988. Can we imagine even bigger islands that should get a label?

[matthijsmelissen]

Thanks for the pull request.

The tag place=island is also quite commonly used for tiny islands/islets, so I think we can change [feature = 'place_island'][zoom >= 14] also to 19 or so. If the island is large enough it will render anyway.

This also does not seem to work on island/islet polygons that also have a natural/landcover tag, but if that is something that needs to be solved, we can do so later.

[sommerluk]

The tag place=island is also quite commonly used for tiny islands/islets, so I think we can change [feature = 'place_island'][zoom >= 14] also to 19 or so.

The downside would be that we do not force people to make a difference between place=island and place=islet. (On the other hand, the wiki is also not completly clear about the difference. There is only a soft description that says that islets have less than 1 km²).

[matthijsmelissen]

The downside would be that we do not force people to make a difference between place=island and place=islet.

I suspect the fact that the renderer rendered island names from z12 might be the reason that place=islet was proposed in the first place.

[sommerluk]

Maybe something to be discussed on the tagging mailing list?

[matthijsmelissen]

I have tested this. We need to take a decision on the [feature = 'place_island'][zoom >= 14] line, and after that I think it can be merged.

[imagico]

In general if the labeling is size triggered you can well start at lower zoom levels - you should however first label place=archipelago then. The french style does this starting at z=4 with quite good results (except for the usual mapnik ugliness) although the size thresholds are very low, see

https://github.com/cquest/osmfr-cartocss/blob/master/placenames.mss#L55
http://tile.openstreetmap.fr/?zoom=4&lat=76.89573&lon=57.71091&layers=B0000000FFFFFFF

where way_area is the area of the convex hull - which is probably not really necessary though.

[sommerluk]

Okay. So we have to decide on the [feature = 'place_island'][zoom >= 14] line and on rendering on lower zoom levels. If we decide this, I can make the necessary changes on this PR.

In the meantime, I’ve played around a little bit with a maximum values for way_pixels. The idea: While it is usefull to have a label on big islands like http://www.openstreetmap.org/relation/3889836#map=9/49.5109/-63.1274&layers=H at zoom level 9, it is probably more distracting than helpful to have a label on z15. So a maximum way_pixels value could maybe be usefull – in order to not render the label anymore when the island occupies the whole screen at some zoom level. Something like [feature = 'place_island'][way_pixels < 99999][zoom >= 7][way_pixels > 3000]. Of course, 99 999 is not big enough. But if I use a greater value than 99 999, it does not work anymore (means: The condition [way_pixels < 99999] seems to have no effect anymore, while the other conditions continue to work like expected). Does anyone has an idea why?

[matthijsmelissen]

Yes, it seems to be a bug in Carto. I run into that as well. See mapbox/carto#370 and mapbox/carto#369.

If you find a way around it, let me know.

[gravitystorm]

I've set the zoom levels to 16 and 17 respectively. We can see how this turns out and adjust as necessary - my feeling was that 19 was definitely too high for pretty much anything, never mind a feature that might be measured in square kilometres but marked temporarily as a node. But like I say, we can adjust if needed.

Thanks @sommerluk for the changes.

[sommerluk]

@math1985

If you find a way around it, let me know.

You could leave one of the way_pixels contions at its place and move the other one into the braces bloc:

.text {
  [feature = 'place_island'][zoom >= 7][way_pixels > 3000],
  [feature = 'place_island'][zoom >= 16],
  [feature = 'place_islet'][zoom >= 14][way_pixels > 3000],
  [feature = 'place_islet'][zoom >= 17] {
    text-name: "[name]";
    [way_pixels > 900000] {text-name: ""; }
    text-fill: #000;
    text-size: 9;
    [way_pixels > 12000] { text-size: 12; }
    [way_pixels > 48000] { text-size: 15; }
    text-face-name: @oblique-fonts;
    text-halo-radius: 1;
    text-placement: interior;
  }

Works, but the code is ugly.