[Tilesathome] close-areas producing very long ways -> inkscape crashing

[Frederik Ramm]

Hi,

> What is actually the reason that not all areas work like coastlines?

There are two important requirements for coastline rendering to work:

1. If the area you are rendering contains coastline, you need to know on 
which side is land and on which is water;

2. If the area you are rendering contains no coastline, you need to know 
wheter it is a water area or a land area.

We have solved (1) by saying what water is always on the right and you 
have to draw your coastline accordingly.

We have solved (2) by using a "tile index" that, for every level-12 tile 
in existence, tells us wheter that is a land or a sea tile; that index 
was relatively easy to create from existing free data. It is a kludge 
because it only works if you look at the world in level-12 units (about 
10x10km) - if I throw a random 5x5km area at you for rendering, then you 
may not be able to determine wheter it should be blue or not with this 
method.

If we want to use this method for all other types of areas - lakes, 
woods, landuse areas, natural reserves - then we would have to find a 
working equivalent to the "tile index" we now have. Let's take the 
example of natural reserves as they are often quite big. Whenever you 
render a tile that does not contain a natural reserve boundary, you 
would have to somehow find out if the whole tile is inside a natural 
reserve. For this, is might not be so easy to create an index - and much 
less so for other areas.

One possible, hacky but promising IMHO, solution is the use of "control 
nodes". This would require you to place (at least) one node somewhere 
into any level-12 tile that is in a natural reserve, tagged (for 
example) "close-areas:landuse=wood". The close-areas script would then 
be extended to have a list of known large area tags, like landuse=wood, 
and handle them like it does coastline now; when it handles a tile that 
does not contain any landuse=wood ways, it would look for a control node 
and if one is found, assume that the whole tile is inside a landuse=wood 
area.

This would clutter our database with "control nodes", but since they are 
only required where there are areas significantly larger than 100 sq km, 
  there shouldn't be too many. (These nodes would only be used where the 
areas in question must be rendered on the slippy map. Anyone is free to 
create an area for, say, the whole of France, but they would not then 
expect any zoomed tile view inside France to have the background colour 
of France or so.)

The disadvantage about this is of course that it is a solution geared 
specifically towards tiles at home rendering. In an ideal world, the 
database server would give you a list of areas that fully contain the 
bounding box you are downloading, but we cannot do that at the moment 
because the database would grind to halt. Anyone willing to design and 
implement API extensions to make this feasible is welcome ;-)

Bye
Frederik