Making Important Farmland Maps

Map Compilation--then and now

The process of making an Important Farmland Map has evolved tremendously in the last decade, along with computer technology and the internet.   Historically, FMMP compiled the land use information on 1:24,000 USGS paper quads, referring to hard copy aerial photos and soil maps, and hand-transferring information.   Processing large GIS files was unwieldy and time consuming, and the hand-transfer of information lead to incremental spatial inaccuracies each time maps were updated.    

Beginning in 1998, FMMP began transitioning the mapping process to a system in which all data sources (digital photography, soil lines, field notations, reference maps) are co-registered and digitizing is done on screen.   This system improves both the spatial and classification accuracy of the Important Farmland Maps; and allows for cross-referencing to other relevant GIS data. The internet has also become a valuable resource for answering questions on land use status, allowing analysts to focus on the most complicated issues in the field.   The transition to the 'heads-up digitizing' workflow was completed during the 2002 update.   Examples of a color infrared air photo and resulting map, in the Hanford area, are at right.  

Soil data has also historically been in paper format, but is now being released in GIS format by the USDA-NRCS.   FMMP completed incorporation of digital soil (SSURGO) data into the Important Farmland Maps during the 2004 update.      

At its core, however, the mapping process is much the same as it has been since 1984: existing maps are compared to new air photos in order to discern land use changes that occurred in the two years between updates. Notes from prior mapping analysts or from outside reviewers are used to document the nature of changes.   Areas that are questionable or that lack photographic coverage are field verified.   FMMP staff review each other's work before new statistics are generated.   The statistics are analyzed to determine anomalies or the need for footnotes.   Finally, new maps are generated and released.      

Aerial photos are obtained from the private sector or governmental agencies. The cost, availability of existing photo coverage, and photo format dictate which photos are actually used in a given update. When possible, color infrared imagery is used due to its superior ability to depict irrigated agriculture. Satellite data are increasingly being used as prices decrease and data quality increases.  

The FMMP staff continues to work on process improvements and look for cooperative opportunities to gather information.   Please contact us to discuss our work anytime!