Policy and Complex Systems
GIS Environment Setup
In our model , the agents are farmers operating farms in the watershed . However , since farm level data are not publicly available , we develop a method to simulate farm level agents from parcel level data . We obtain three sources of geographic information system ( GIS ) data for the Murderkill River watershed : ( 1 ) Parcel level size and location data for Delaware ; ( 2 ) Watershed boundary data for Murderkill watershed ; and ( 3 ) National Land Cover Database ( NLCD , 2011 ). We combine these three data sources together to generate an estimate of the agricultural land for each parcel in the watershed .
Agent Initialization
By combining parcel-level GIS information with data on land cover for this watershed , we can estimate the amount of land used for agriculture within each parcel and the X – Y coordinates of the parcels . Since farms often consist of a constellation of parcels and we do not have data on the actual allocation of parcels to specific landowners , we initialize the size of each farm based on the probability density function from data from the 2012 Census of Agriculture ( U . S . Department of Agriculture , 2012 ) for Kent County , Delaware . Using that information and the GIS information , we match a simulated landowner agent to various numbers of parcels . In this process , we first calculate a “ distance matrix ” that contains information on the geographic distance between the individual parcels and every other parcel in the watershed . We then create landowner agents by grouping the nearest neighboring parcels until they meet criteria identified by the probability density and average size of each category of farms in the Census of Agriculture . The result is that our agents constructed from neighboring parcels closely mimic the census data on farm size distributions . Figure 2 displays the farm size distribution of Kent County , Delaware , and Figure 3 shows our simulated farm size distribution .
Figure 2 . Census farm size distribution of Kent County , Delaware , USA .
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