ophz's Introduction

Open Plant Hardiness Zones (OPHZ)

UPDATE: As of April 2017, the official PHZ data is no longer behind a paywall. Grids, shapefiles, and zipcode listings are now downloadable directly from the PRISM Climate Group. However, the OPHZ data available here, at approximately 450m pixel resolution, is higher resolution than the 800m pixel grids available at that site.

OPHZ is free and open raster and vector data derived from the public domain map images available at http://planthardiness.ars.usda.gov/

In the original public domain PDF map (305MB!), there are some gaps due to rivers, borders, and coastlines. OPHZ fills most of these gaps with the nearest values.

OPHZ currently covers the 48 contiguous US states (US48), and is available in the following formats:

shp - national polygon shapefile
geojson - polygon geojson files (one for each state)
topojson - national topojson file
tif - GeoTiff raster, two versions:
- ophz-us48.tif - Each colored pixel of the original map image has been translated to a value representing lower end of the corresponding zone's temperature range. Most gaps have been filled with the nearest data value.
- ophz-alpha-us48.tif - For those who want the original, unfilled raster with no interpolation of nodata values. International borders, coastlines, and a few major rivers appear as -98. Open water is -99.

All vector formats are in WGS84 (EPSG:4326), and the raster formats are in the original Albers projection (EPSG:5070).

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Alaska and Hawaii

Process Alaska and Hawaii, making the AK and HI rasters available as separate GeoTIFFs (no need to have all those empty ocean pixels), but add the vector polygons to the US48 shapefile, geojson, and topojson files.

Embed colors in GeoTIFF

Assign standard temperature colors to the data values, so the .tif image will display in appropriate colors by default.

But this might not actually be possible with the range of data values (-40 to 40 step 5). Using GDAL, at least, it seems that data values must range from 0 to 255.

available data formats

Reconsidering the original ophz-a, ophz-b, ophz-c options, I think they will tend to confuse most users of the data. I still think ophz-a (original raster values, with no tinkering to fill gaps) is valuable to keep (perhaps as a starting point for other versions filled by other methods), but most people will probably want a more complete, filled layer with fewer gaps, and that version should simply be referred to as "ophz".

ophz will refer to the gap-filled version, and should be available as:
* US48 .tif raster (in Albers, EPSG:5070)
* US48 .shp vector polygons (WGS84, EPSG:4326)
* state .geojson vector polygons (WGS84, EPSG:4326)

ophz-a (or ophz-alpha?) will still refer to the original raster values extracted from the PDF.

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