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<p class=MsoNormal>The state of California has some good landcover shapefiles
on the<br>
Department of Forestry and Fire Protection site. They are sorted by<br>
county. The smallest are under a meg while the largest - Fresno - is more<br>
than 400 megs. The average size is around 30 to 40 megs. These would be a<br>
great addition to OSM since they contain valuable metadata. Once the<br>
areas have been added, the state will take on a similar look to states<br>
like Georgia and Massachusetts that have<br>
had statewide imports done. Another good example of what California can<br>
be is the Corine Land Cover (WikiProject Corine Land Cover).<br>
<br>
There are several challenges with the data. Here are a couple.<br>
* It is a huge dataset and will need some optimization. The straight<br>
lines have points every five meters, creating jagged edges that<br>
aren't visually attractive. Josm has a plugin but that's probably not<br>
the best way. A spline interpolation would really improve it<br>
dramatically. It will increase data size, but it's worth it. Maybe<br>
there is a batch mode program available to do that. Mapshaper has a<br>
tool to optimize a shapefile by reducing the details in the file. It<br>
may not be working though. Here is a rough idea of what the areas<br>
look like without being simplified.<br>
<br>
* Only vegetation data should be used. The<br>
urban/residential/water/unknown should be skipped since the quality<br>
isn't good enough for this purpose and would just create tons of<br>
conflicts with existing data. Also there is/will be better data<br>
available.<br>
<br>
* We can use some filters to split the shapefiles into different<br>
features. This is also great to prepare the OSM files for each type<br>
instead having it mixed all together.<br>
<br>
* All these polygons have overlapping ways. This should be avoided<br>
because it creates tones of duplicate nodes/ways. Each polygon should<br>
be split in single ways and the area defined with a relation.<br>
According to the description, mapshaper will do that to. There may be<br>
a way to do this with postgis or through a Perl script. Validator<br>
will just merge duplicate nodes, but can't fix duplicate lines. This<br>
is really a tricky thing that many other updates lack. Efficiency<br>
should be considered here. Also editing is easier then. This data<br>
shouldn't need much editing after import.<br>
<br>
Please feel free to add your comments and suggestions on the California Land
Cover wiki page. This is also being posted to the<span style='color:#1F497D'>
talk-us </span>list.<o:p></o:p></p>
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