Don't forget, tomorrow night is Building Mapping night. Have you done your homework yet?
I did mine last week (teacher's pet), and I notice a couple of other people have sketched theirs. Slapping in building outlines quickly using Yahoo! imagery can feel a little bit careless, particularly given its overbearing rendering style. It's a high impact kind of mapping, without the effort of doing any real mapping, which all feels a bit wrong.
Of course we are going to try to do some real mapping tomorrow night, to double-check building outlines where the imagery wasn't clear. It remains to be seen how effective that will be.
My experience was that the most unclear aspect of building outlines is more to do with how buildings back onto eachother in areas off the main streets, which probably don't have pedestrian access anyway. Many city blocks appear to be composed of a large number of small interlocked buildings, judging by the rooftops. Should these be intricately mapped as separate areas or lazily sketched around as one area per block?
But in general I'm thinking let's not worry about it too much in the first instance. Edit with confidence. It's a wiki after all. We can refine building outlines over time. As I said before, it's always good to get some first hand experience of doing before discussing mapping, but maybe tomorrow's meet-up can be a time to discuss the best mapping approach for buildings.
Whether or not you're on board with the building outlines homework idea, feel free to come along and join us tomorrow night near Oxford Street (meet-up details)
Discussion
Comment from IgnoredAmbience on 15 September 2009 at 20:22
My changeset gives my feelings http://www.openstreetmap.org/browse/changeset/2487807 but, then look at the timestamp for an idea why.
Thanks for expressing the very things I was thinking last night.
Verifying the outlines is going to be an interesting challenge.
I was considering doing a central london survey for the whole day, mostly focusing on naptan tidying. However, I need to find a method for taking the existing data out into the field for comparison...
Comment from Harry Wood on 15 September 2009 at 22:21
Yeah. I noticed your area looking nicely sketched out. Looks like you've gone for lots more detail than me. Must've taken a while!
I'll explain my thinking a little more.
Buildings outlines would ideally be mapped either not at all, or completely and whole-heartedly (like in Helsinki). The only decent middle-ground would be based on some sort of importantness metric. That approach works well for many maps, but maybe it's too subjective to work well in OSM.
In London we've just ended up with a disorganised hotch-potch of building outlines. It's easy to see how this happened. It's a massive city. Sketching building outlines is tedious. Surely it could never be done across the whole city, and so nobody attempts it. Instead though we have a handful of important buildings sketched in, plus a handful of buildings which happen to have interesting outlines. Then in outlying areas we have funny little clutches of building outlines for concrete housing estates. This is because they're really difficult to map in any satisfyingly complete way without showing the buildings. These are the worst offenders though, because they are not important buildings by any stretch of the imagination. Then more recently we've had the likes of Dave & Blumpsy battling for completeness supremacy with really beautifully complete building outline mapping along with housenumbering in their areas.
Nobody's intentionally damaging the map, but when you zoom out and look at it, we've collaboratively created a rather ugly imbalance. The London mapping party gang are in a good position to experiment, discuss and figure out a way forward.
Comment from marscot on 16 September 2009 at 09:49
I have started using the tags building:height building:roof:shape building:roof building:use and building:levels which are the 3d model tags used to make it so.
Comment from Wynndale on 16 September 2009 at 11:33
I’ve hit a snag: a previous mapper outlined the tower bit of the Telecom Tower leaving out the low buildings around it. If I fill everything in Helsinki-style the arguably-interesting outline is lost.
Comment from IgnoredAmbience on 16 September 2009 at 12:59
We obviously need a building_importance=very tag to make them show up in bright red...
Comment from IgnoredAmbience on 16 September 2009 at 13:00
Oh, and I'm sorry I can't make tonight, would have loved to talk about this more, but double-booked myself :(
Comment from Harry Wood on 16 September 2009 at 14:35
@Wynndale yeah I see what you mean. Actually I pondered that problem when mapping around the BT tower before. One to discuss in the pub I guess
@Edgemaster Shame you can't make it. Next time then!
Comment from marscot on 16 September 2009 at 20:55
I think the layer tag used with building would help if it was able to render the layer 1 over layer 0 or where there is no layer tag used.
so the tower would be building=yes layer=1
other building next to it building=yes layer=0
but just now that does nothing.
Comment from Harry Wood on 17 September 2009 at 00:22
Yes layer could be a solution, but I think osmarender is better at handling layer tags than mapnik at the moment