View source for Find majority county coverage in model grid cells


==Question==

How do I figure out which grid cells (x, y) contain any part of the Chicago ozone nonattainment area?

==Approach==

Use a GIS to find the counties that intersect the model grid cells.  

==Details==

===Create a shapefile of the 12US2 modeling grid (396x246) ===
Use the [https://github.com/CMASCenter/Spatial-Allocator Spatial Allocator] raster tools to create the shapefile. See generateGridShapefile.csh script as an example.

   setenv GRID_PROJ "+proj=lcc +a=6370000.0 +b=6370000.0 +lat_1=33 +lat_2=45 +lat_0=40 +lon_0=-97"
   setenv GRID_ROWS 246
   setenv GRID_COLUMNS 396
   setenv GRID_XMIN  -2412000.0
   setenv GRID_YMIN  -1620000.0
   setenv GRID_XCELLSIZE 12000
   setenv GRID_YCELLSIZE 12000
   setenv GRID_SHAPEFILE_NAME ../output/conus_12US2.shp
   ../bin/64bits/create_gridPolygon.exe 

===Add X Y columns to the shapefile===

# Load the CONUS12 shapefile into QGIS.
# Open the attribute table, put the file in edit mode, and add two short integer columns: X and Y
# Apply the following field calculator formulas, in this order (calculate Y first), to calculate X and Y; note that 396 = NCOLS

   Y = (floor(("GRIDID"-1)/396)+1)
   X = "GRIDID"-("Y"-1)*396

===Intersect the county and grid shapefiles using GIS ===

Use the QGIS Intersect function to find all counties that intersect each grid cell. 

1. Load a county shapefile into QGIS

[[File:CountyMap.png|800px]]

2. Load the grid shapefile and put the county shapefile and model grid shapefile on the same coordinate system

[[File:County-grid.png|800px]]

3. Use Vector->Geoprocessing Tools->Intersection to intersect the two features.  The grid shapefile is the Input Layer; the county shapefile is the Intersect Layer

[[File:Intersect.png|800px]]

== Results ==

=== [https://drive.google.com/uc?export=download&id=1U-AoHnpTAfNKc1uAU_moUlleyYUkWRUX Download a CSV file with county and grid cell intersection] ===