Tuesday, October 21, 2014

Metadata

A shapefile is a common vector data format, originally developed by ESRI. The shapefiles provided in the Shapefile zip have been modified from the original, authored shapefiles. All topological errors are resolved before any processing occurs. The files have been merged into one dataset where each DM class is represented by one polygon. The files have been projected to the USA Contiguous Albers Equal Area Conic projection. Finally, the dataset has been clipped to the United States boundary (provided by the U.S. National Atlas). Metadata for each shapefile is provided in the zip file in the *.shp.xml file. For more information regarding the original, authored shapefiles, please contact Brian Fuchs at the NDMC via e-mail.

Please note, shapefiles prior to 2004 have been digitized from the image archive. Preliminary error analysis indicates that the digitized datasets have a horizontal error of approximately 4 miles when compared to authored datasets. For comparison, the drought impacts line in a georeferenced image is approximately 12 miles wide.

The shapefiles provided in the Impacts zip have not been modified from the original, authored files. Each zip can contain up to four different shapefiles:

  • Drought_Impacts_US
  • Drought_Impacts_Type
  • Drought_Impacts_Callout
  • Drought_Impacts_Lines

Drought Impacts_US is a polygon shapefile containing the spatial information for the impacts depicted on the main Drought Monitor map. In some cases, the impacts are depicted as a single line. If this occurs, the zip file will also contain the Drought_Impacts_Lines shapefile. The Drought_Monitor_Type shapefile is a point shapefile containing the named impact information for the hydrological and agricultural drought indicators. Finally, the Drought_Impacts_Callout shapefile contains the callout lines for the indicator labels. For example, if multiple islands in Hawaii are labelled agricultural drought (A) but only one label is used, callout lines are used to point to the islands involved. These are provided solely for display purposes. If the projection is undefined for these files, please use the USA Contiguous Albers Equal Area Conic projection.

KML files are spatial datasets formatted for Google Earth. The KML files are generated from the cleaned shapefiles described on the Shapefiles tab. Each file contains one Drought Monitor layer and a metadata text file. The metadata is based on the cleaned shapefile and is provided for information only. Projection is based on the Google Earth spatial reference. The symbology for the drought classes is the same as that found on the Drought Monitor images.

In the digitized datasets (years prior to 2004), the shapefile has been simplified before generating the KML file to fall within the maximum number of points allowed. The cleaned shapefile has not been simplified.

GML files are spatial datasets formatted using the Geographic Markup Language. These files can be used on a variety of GIS platforms. The GML files are generated from the cleaned shapefiles described on the Shapefiles tab. Each file contains one Drought Monitor layer, a schema, and a metadata text file. The metadata is based on the cleaned shapefile and is provided for information only.

OGC Web Mapping Services (WMS) are web services that provide georeferenced map images to a variety of clients. Each WMS file contains one Drought Monitor layer based on the cleaned shapefiles and reprojected to the WGS84 projection. Basic metadata can be found in the WMS metadata section.

WMS services can be accessed through any desktop or web client that supports WMS 1.0. The services are served using the EPSG 4326 projection code. For those users wishing to incorporate the Drought Monitor in Google Maps with the WMS, change the SRS parameter to EPSG:900913 (the Web Mercator Projection). Adjust the BBOX parameters accordingly.

The Excel files contain the percent area statistics for the given week. The Drought Monitor classes are cumulative---if a region is in D2, it is also in D1 and D0. The statistics provided on the site represent those cumulative values. For example, Region A has 75% in D0, 50% in D1 and 10% in D2. 25% (75%-50%) of Region A is in D0 only; 40% in D1 and D0; and 10% in D2, D1 and D0.

Each file contains four worksheets:

  • one containing values for the whole U.S. including Alaska, Hawaii and Puerto Rico (total)
  • one containing values for the contiguous U.S. (conus)
  • one containing values for each state (state)
  • and one containing values for each counties (county)

Column headers are included. Note that the column header D2, for example, actually contains the value for D0-D2.

The Drought Monitor color scheme is as follows:

CategoryRedGreenBlueCyanMagentaYellowBlackHueSaturationValueHex
D0 25525500.0000.0001.0000.00060100100#FFFF00
D1 2522111270.0000.1630.4960.012404998#FCD37F
D2 25517000.0000.3330.0000.00040100100#FFAA00
D3 230000.0001.0001.0000.098010090#E60000
D4 115000.0001.0001.0000.549010045#730000

For ESRI users, please download the Drought Monitor layer file (Drought_Monitor_Lyr.zip). The layer file can be applied to any shapefile downloaded from the GIS Data page. Open the Properties window and go to the Symbology tab. Select Categories>Unique Values. Click Import and navigate to the Drought_Monitor.lyr file from the downloaded ZIP. Set the Value field to 'DM' and apply. If you receive a "geometry type" error when trying to apply the layer symbology, please visit:

http://support.esri.com/index.cfm?fa=knowledgebase.techarticles.articleShow&d=22484

and use one of the shapefiles from our site as the data source.

Font Colors

For best contrast and readability, it is recommended to use a black font (#000000) on top of the D0, D1, and D2 colors and a white font (#FFFFFF) on top of the D3 and D4 colors.

Please cite the Drought Monitor by including the National Drought Mitigation Center (NDMC), the U.S. Department of Agriculture (USDA) and the National Oceanic and Atmospheric Association (NOAA).

For more information about any of the Drought Monitor datasets, please contact Brian Fuchs at the NDMC via e-mail.

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