Does anyone have thoughts on why a Philadelphia label does not show on openstreetmap.org at zoom level 6 and 7 (example)? I would expect it to, given the population and land area, so I would like to fix this. Other less-populated cities do show at zoom level 7.

Interestingly, it does show at zoom level 5.

(P.S. I realize this has been asked before. It was first asked in an confrontational way and closed as such, then closed as a duplicate of that. Before closing, please consider that I am trying to address this constructively, and AFAICT it has not been answered yet.)

asked 14 Dec '15, 02:59

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mattflaschen
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edited 14 Dec '15, 06:32

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aseerel4c26 ♦
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This question has been asked before, albeit not as considerately as this time.

The basic answer remains the same: this is an artefact of the label collision algorithm of Mapnik. Philadelphia/Camden is just one of many examples.

There are OSM-based maps which do much more pre-processing to support label placement: one example is mapsurfer.net (see Philadelphia here, and note that Camden does not appear until well zoomed in). The standard OSM map is built for speedy update and therefore tends to eschew pre-processing of the data.

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answered 17 Dec '15, 10:42

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SK53 ♦
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Thanks for the explanation. I hadn't seen OpenMapSurfer before. I will keep that in mind.

(26 Dec '15, 02:50) mattflaschen

Note mapsurfer seems to be no longer active.

(02 Jun, 14:27) SK53 ♦
  1. Check and get the data right ( http://overpass-turbo.eu/ helps to easily find the objects – centre the map, use the wizard and type in name=Philadelphia). I do not really see issues (except that the place=city exists twice for Philadelphia – once as node and once as relation). That seems to be quite common for cities but IMHO not right. Questionable if the duplication could cause this label issue (likely someone else here knows). If we assume the data to be right, then the cause is the label placement:
  2. Ask the map style makers if the label placement/collision handling (this is automatic) could be improved. This may need adjustments/new programming at the map renderer (mapnik). See how-to-move-labels for a bit about label placement.
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answered 14 Dec '15, 06:04

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aseerel4c26 ♦
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edited 14 Dec '15, 06:36

Camden seems to have a larger area than Philadelphia which may explain why it gets displayed for two zoom levels but i have no idea why that only occurs for only two levels.

(14 Dec '15, 21:53) andy mackey

@andy mackey: Perhaps because there are also other labels crowding it out ("New Jersey" at both zoom levels)?

(15 Dec '15, 15:18) Piskvor

The duplicated place element (node and relation) has been discussed at other places multiple times. Unfortunately I don't have a corresponding link but as far as I know one reason for this accepted practice is that the node is really helpful for routers to determine the city center.

(16 Dec '15, 08:27) scai ♦
1

Are labels rendered at all from place ways/relations? I don't know sql well, but reading (https://github.com/gravitystorm/openstreetmap-carto/blob/master/project.yaml#L1466) I get the idea that only place nodes are used for labels. I guess there could be something at an earlier stage that generates place nodes from polygons, but I think I've added place nodes to towns to get a label showing.

I looked at the issue when it came up in a non osm discussion and ended up where Piskvor is, speculating that there were collisions at some zooms.

(16 Dec '15, 16:24) maxerickson

@scai: thanks! The city centre could be made up by looking at the admin_centre member of the city relation (e.g. https://www.openstreetmap.org/relation/62400 ). For this the node itself does not need the place tag again (in this example it currently has, yes). As said, I rather don't think that this is the cause for the label problem in this discusion.

(17 Dec '15, 05:58) aseerel4c26 ♦
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question asked: 14 Dec '15, 02:59

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last updated: 02 Jun, 14:27

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