[OSM-talk] Mapping everything as areas

[Steve Bennett]

On Sat, Nov 28, 2009 at 10:08 PM, Richard Bullock <rb357 at cantab.net> wrote:
> For renderers:
>
> *    nearly all maps exaggerate road width except when really zoomed in. A
> 30-35 metre wide motorway would appear almost insignificant at z levels less
> than 10 or 12 - but this is precisely the opposite of what we'd want;
> motorways should be significant roads when zoomed out. You'd have to find a
> way of expanding the areas to make these more significant.

Maybe I missed the crucial bit, but presumably any area=yes highway
has an implicit line running down the middle of it. The renderer would
use that line at lower zoom levels exactly as it uses any other line.

This does all assume that the area really does behave like a line. If
people get creative with T shapes or whatever, then it would break
down.

> For routers:
>
> *    routing over areas is much harder than routing along ways between
> nodes. Directions are not defined so one-ways are meaningless. You could do
> routing over areas, with some pre-processing, but it would 'break' a number
> of existing established routers

I was thinking about this before, surely you can directionalise an
area by defining a start *way* and an end *way* just as a line has a
start node and end node. Again, assumes an area that is still kind of
linear in shape.

> In summary, I have no problem with people mapping everything as areas;
> however, I believe for the moment we will have to use both areas and ways.
> Most wide rivers mapped as areas I've seen also have a way down the
> centreline - to define the river name, and direction of flow. More
> importantly, using both ways and areas would render the way we'd expect;
> wider when zoomed out because the way is rendering wider than the area;
> wider when zoomed in because we are seeing the visible extent of the area,
> and we can have street names rendered in the right direction down the

Yep, it seems to work well in practice, too. A map that is all areas
and no lines isn't really a map anymore, it's a floor plan or a
diagram. Maps intentionally simplify the real world, to make it easier
to understand.

> centreline. For routers we can continue to follow the ways as "navigation
> paths", ignoring areas, and we can define the direction of travel for
> one-way streets.

Surely a good router would find paths within areas that are not along
its boundaries...?

Steve