I have downloaded the maps of the British Isles (routable, with contours) from Talkytoaster's very useful web site (http://talkytoaster.info/ukmaps.htm). The MapSource version shows Bronwich Pond (http://www.openstreetmap.org/?lat=50.83241&lon=-1.26315&zoom=15&layers=M) as a lake, but the Garmin GPS version renders the pond as woodland. The GPS knows that the pond is there, as the land description changes from Woods to Lake when the cursor is moved over the pond. Another small lake (at long -1.255, lat 50.842) shows the same problem, but other small lakes in the same area render correctly on both versions of the map. I had intended to correct the problem, but looking at the OSM data in Potlatch 2, I can see no difference between the mapping of the ponds that render correctly and the ones that do not. Can anyone help?

asked 18 Apr '12, 22:35

Madryn's gravatar image

Madryn
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edited 19 Apr '12, 08:21

Putting the ponds into multi-polygon relations with the surrounding woods seems to have corrected the rendering on the GPS. Thank you to the people who suggested it.

(27 Apr '12, 23:34) Madryn

As noted by gnurk, these areas overlap each other - so different renderings will draw things in different orders and only one may come out on top of such conflicting area types of water and forest.

Luckily with my new found Potlatch 2 shortcut and usage++, I think I've been able to fix it with this edit to set it to multi-polygon relations (and other ponds/lakes nearby): http://www.openstreetmap.org/browse/changeset/11349850

Obviously you'll have to wait for Talkytoaster's rerendering (normally every week or so) for the update.

+In Potlatch 2, first select the outer (i.e. surrounding) area - then select with a control-click the inner area so two areas are selected. Then press 'h' and voila the multi-polygon relation is created. Unfortunately Potlatch 2 doesn't colour in the inner area blue. Hopefully normal mapnik renders (and Talkytoaster's) will.

Edit: In fact the order of selection shouldn't matter as Potlatch2 is clever enough to work out which is the larger outer and small inner areas.

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answered 19 Apr '12, 01:44

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robbieonsea
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accept rate: 16%

edited 23 Apr '12, 01:18

1

uiii! I must try the h-shortcut once! That sounds really straightforward!

Edit: Works excellent!

(19 Apr '12, 14:38) moszkva ter

Thanks for your answer. Could I ask you to look at Abshot Pond (http://www.openstreetmap.org/?lat=50.8494&lon=-1.266458&zoom=18&layers=M),which renders correctly on Mapsource and on the GPS, but which does not seem to be part of a multipolygon relation with the surrounding woods. Is that just luck?

(21 Apr '12, 10:02) Madryn

I've just made it a multipolygon (I thought that was your request). Now I reread your question, yes I guess it was luck - there must be other factors that can affect the rendering layering - but I can't see what they would be for this instance.

(23 Apr '12, 01:16) robbieonsea

The Bronwich Pond is completely covered by the surrounding landuse=forest-area so that's probably the reason why it's rendered as forestration in some maps. The problem had most likely not occurred if someone had put the pond in a hole in the forest (using a relation in OSM).

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answered 18 Apr '12, 23:06

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gnurk
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question asked: 18 Apr '12, 22:35

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last updated: 27 Apr '12, 23:34

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