Hm... this polygon type (0x13) is not documented in the garmin_feature_list.csv file in the mkgmap resources directory, is it? Where did you find it?
I found it in the cgpsmapper manual - it seems to have more Garmin codes than the garmin_feature_list.csv file. You can find it here:
http://www.cgpsmapper.com/download/cGPSmapper-UsrMan-v02.4.3.pdf
I just stumbled over another list of types. Its contained in the cookbook for the maptk programm. (Available only in german) http://www.maptk.dnsalias.com/Docs/Kochbuch.pdf
I tried out a somewhat different approach for for squares and plazas: I found an unused polygon type (0x1b) and added a tiled bitmap for this polygon to the TYP file I use. The bitmap, with a lot of imagination, represents what I could picture as a flagstoned or cobblestoned area. As well, I added 0x1b to my polygon style file.
There is the polygon type 0x1b (page 40) described as pedestrian. So you have choosen a good one :-)
However, I'm not sure what consequences these polygon types would have for pedestrian/bicycle routing. It would be inconvenient if pedestrians were always routed around plazas and squares as if these areas were impassible obstacles.
That's actually a good point. Giving it a little thought here ... Even if these area were marked as a park, would pedestrians be routed through the area in any direction? That definitely doesn't make sense for the parks or squares I know here in San Jose. I would rather specify the paths in the parks and have the pedestrians routed through those. Thoughts?
In the file there is also mentioned a line type 0x0d for pedestrian areas. (page 39) Maybe we need to insert a routable line behind the polyogon?