[OSM-newbies] layers in OSM?

[Serge Wroclawski]

On Sat, Sep 4, 2010 at 3:09 PM, Xan

>>> What is your use case?
> Can I choose the three? :-)

No. :-)

> What are the technical details of these? Can you give me an sketch.
>
> My intention was to user has the possibility of choose "layer of things
> he/she wants": for example: shops+rivers. And good if he/she could edit the
> items displayed in that layer (only shops and river in this example).
>
> Is it very difficult to do it?

It depends on what you mean by display, honestly.

> With this OSM act, also, as a service:
> - which bus_stop is the nearest of the cemetery of Palma of Mallorca? I

> - Wait. Consult OSM and choose "display customized layer" and check
> bus_stops and wooala!! only see the map.

There's a lot here, so I'm going to stay somewhat high level (read:
oversimplified) and also stay pretty close to the use-case level,
rather than diving into technical details.

Let me start with what I sometimes do for editing.

When I'm editing, I often am interested in one or two features. I know
the map contains lots of things, but I only want to see things I'm
working on.

Each editor will do this a bit differently, but Josm and Potlatch 2
offer relatively simple methods to do this. In Josm, it's called
Filtering (http://josm.openstreetmap.de/wiki/Help/Dialog/FilterDialog)
and in Potlatch 2, you can create a custom MapCSS file with just the
items you care about. I mostly use MapCSS to do this kind of
filtering.

So if that's your use case, that's what you can do.

If you're looking to make a custom rendered map, this is a bit more
complex. You need to tell the renderer to only represent certain
items.

The short answer for this is, you have roughly two options. First is
to use a commercial service like CloudMade to make your own custom
maps, or you can run them yourself. CloudMade has a custom map style
editor and then you can make your map the way you want it.

You could also make your own service like the one you describe where
people could enter their own renders on the fly, but be aware that
this is both disk and computationally expensive.

OSM doesn't run this type of service, I suspect for a few reasons. One
is that, as I mentioned, providing such a service would be both
storage and computationally intensive. Doing on the fly renderings
like that would place a burden on the system. Secondly, there are
options for other providers (including commercial providers) to step
in and provide that service for users, if they want/need it. And
thirdly, because the data is available, if a user needs that, they
could certainly provide it to themselves given a little time and the
technical knowhow.

Lastly, you mentioned querying. This doesn't sound much like you want
a visual representation, but you want to ask geographic questions to
the system and get an answer, and I'm afraid I don't know of any
service like the one you're talking about, though it wouldn't be very
difficult to write. In fact it may exist and I don't know about it,
but you could certainly take the data, put it in a database and then
run queries against it.


I hope that answers your question.

- Serge