The California State Department of Conservation Farmland Mapping and Monitoring Program (FMMP) has given OpenStreetMap permission to use their farm data under a public domain license. They just request attribution. To comment about the proposal, go to http://wiki.openstreetmap.org/wiki/California_Farms.
We should import the new 2010 data when it comes out hopefully by the end of the year. Currently just the 2008 data is available. The data can be posted and then people who are familiar with the areas can download them, clean them up in JOSM and then upload. They should compare the FMMP data with the existing data and then replace the old farm data with new farm data when possible.
We should use this data set for importing just the farmland. The other land areas, urban lands and grazing areas could come in handy when needing to add a zone to a city that hasn't been zoned but in general shouldn't be used. The water layer should also be avoided because the NHD import is better.
This data is included in the California Land Cover import, but this data is more accurate and should be done first before that import is attempted.
Updating- The data is updated every two years. FMMP is looking for a way to be able to update the data when it is changed and also to see what changes have been made. They would also like to be able to contribute back to OSM and in turn be able to reference the data from OSM when it changes. There currently aren't any good methods to be able to sync the data.
Alignment- FMMP data is slightly misaligned and appears to be off when viewed with aerial photos or OSM data. FMMP is saved in NAD27 and would need to be converted to WGS84. While the data is generally good, it's almost as if the whole layer needs to be shifted slightly to make it align. It could simply be a matter of the projection conversion. Maybe there is another way to automatically convert it.
Crossing layers - Some layers may cut across a field that looks like it should all be one area. FMMP classifies farm data as prime farmland, farmland of statewide importance, farmland of local importance or unique farmland.
Lack of details - OSM is detailed when it comes to farms. There are vineyards, orchards and farmland among some of the variations in farms. FMMP makes no distinction between what the land is used for, with the exception of grazing, which isn't useful in OSM because it is too general.
Existing data- Some counties such as Fresno, Kern and Santa Cruz already have farm data imported on the parcel level. If the FMMP data was added here, it would have to be combined with existing data.