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4. Calculating Constrained Acres


Now we will deal with constraints layer(s) (floodplain, excessive slope, etc.). Note: If you had no constraints, the tool is ready for analysis.

For this section, add your Constraint layer (found in the 4_Constraints folder), Constraint1, to the Table of Contents.

  1. First, Constraint1 needs a field for Acreage (TOT_ACRE), so we will have to create one as demonstrated in Tutorial 1. 

    Link to Tutorial 1

  2. Next, in ArcMap, click Geoprocessing>Union and select the ET_Vision1 layer and the Constraint1 layer as the Input Features and under Output Feature Class, enter Polygrid_Union. Click OK.

    You now have a shapefile that is a union between your constraint and polygrid layer.

  3. In the newly created Polygrid_Union layer, recalculate the TOT_ACRE field. Click OK.

    Also, repeat that process for ET_Vision1's TOT_ACRE field.

  4. Join the ET_Vision1 layer to the Polygrid_Union's layer table using a common unique ID. Right-click on ET_Vision1 and select Open Attribute Table.

    Then Click on Table Options and go to Join and Relates> Join... 

    In the Join Data menu, in Field 1, select OBJECTID. In part 2. Enter Polygrid Union and for part 3, enter FID_ET_Vis. Click OK.

    If you are prompted to create and index, select yes. Now your two layers are joined. 

  5. With ET_Vision1's attribute table still open, right-click on the CONSTRAINED_ACRE field and select Field Calculator. 

  6. In the Field Calculator Box, set ET_Vision1's CONSTRAINED_ACRE field equal to the ET_Vision1's TOT_ACRE minus Polygrid_Union's TOT_ACRE.

  7. Now remove the join. Right click on ET_Vision1 and select Joins and Relates>Remove Join(s)>Remove All Joins.

  8. Now we need to update our VAC_ACRE and DEV_ACRE fields because of the extra calculations we've made. First, we deal with VAC_ACRE, use Select by Attributes in the attribute table and select all rows where VAC_ACRE >0.

    Now select Show selected records and use Field Calculator to set VAC_ACRE equal to TOT_ACRE minue CONSTRAINED_ACRE. Click OK.

  9. Next, do the same with DEV_ACRE. First, clear selected features. Then, using Select By Attributes in the attribute table select all rows where DEVD_ACRE >0. 

    Now select Show selected records and use Field Calculator to DEVD_ACRE equal to TOT_ACRE minus CONSTRAINED_ACRE. Click OK.

Now your scenario layer is ready.

Final Preparation

Now we need to create multiple scenario layers from our prepared ET_Vision1 feature class.

1. First click on the Catalog button at the top of the menu.

2. Navigate to your File Geodatabase and then right-click on the name. Go to Import>Feature Class(single)

3. Now you are going to import the existing feature class back into the same geodatabase to make copies.

4. In the end you should have as many feature classes, as scenario layers. Here I made four: