making efficient map layers

[Stephen Woodbridge]

Mark Dieterich wrote:
> Steve,
>
> I'm really impressed with the maps on the imaptools site, hope you don't
> mind a few prodding questions from a mapserver newbie...

Thank you, it is an ongoing project. The mapfile has 45 layers and about
1900 lines in it. I recommend that you keep it simple, get the basic
logic of the mapfile working with the zoom levels you need. Some of the
mapfiles I have built have had over 150 layers in them and it gets very
hard to keep it all straight.

> - Does your site actually use some form of generalized layer when zoomed
> out?  If so, can you tell me at what point you switch from generalized
> maps to shapefiles, it seems really seemless.

I switch at 150000 scale so below that it is Tiger and it is my own
generalized Tiger layer above that.

> - How do you go about changing the width of the different types of
> roads?  I assume each class of road is in a different layer and you
> somehow manipulate the line width?

In your class for the roads do something like this:

CLASS
   EXPRESSION ...
   STYLE  # first draw a 5 pixel wide green line
     SYMBOL 0 # built in circle symbol
     SIZE 5
     COLOR 0 255 0  # green
   END
   STYLE  # then draw a 3 pixel wide white line on top of the green
     SYMBOL 0   # that leaves a 1 pixel border on each side of the white
     SIZE 3
     COLOR 255 255 255  # white
   END
   STYLE  # then draw a 1 pixel wide black line down the center
     SYMBOL 0
     SIZE 1
     COLOR 0 0 0  # black
   END
   ...
END

You can create your own symbols to do dashed lines, put arrows on lines,
create railroad dual tracks with cross ties, etc.

> - Is there any speed reason to split types of roads, based on the CFCC
> type, into different shapefiles or is it just as good to use shp2tile

I split them because there are a lot of A4* streets and I can avoid
using a CLASS EXPRESSION if they are all in their own shapefile which is
marginally faster.

> and then a tileindex?  On a side not, is it possible to throw a wildcard
> at ogr2ogr, where by you can specify something likek ogr2ogr dst.shp
> src.shp -where CFCC=A1*?  I couldn't figure out if it could take
> wildcards or not.  I suppose you could go through and run it for each
> A1* type and append it to the shapefile, but this could be a long process.

Great question, I will leave this for the ogr experts to answer because
I haven't a clue.

> I'm working on familiarizing myself with the National Map offerings and
> will probably have some more questions for you.
>
> Thanks!
>
> Mark
>

-Steve
  http://imaptools.com/