The Select tool, when operated from within ModelBuilder, has a problem in that it always changed the SQL term 'Not prime farmland' to 'Not Prime Farmland'. This caused none of those features to be selected, because the lower-case letters had been changed to upper-case, and so were not recognized. The Erase too
l then had nothing to erase, because the Select tool had found nothing to select. Strangely enough, when the single quotes around Not prime farmland were changed to double quotes, and the model run (with errors, because it didn't like the double quotes), and then the whole SQL statement was entered again, the lower case letters were preserved in the model, and it could run correctly. Some other people also had this problem and brought it up on this week's discussion board, and found that removing the quotes completely from Not prime farmland, and then putting them back, also fixed the problem.
The model was then converted to a Python script, and a few adjustments were made, such as adding the full file path to the input shapefiles (soils and basin) so that the script could find them, and also adding the line of script arcpy.env.overwriteOutput = True. This makes it possible to run the script multiple times, although the outputs already exist in ArcCatelog from previous runs. The Python script can then be converted into a Script Tool within ArcMap, where it can be run like any other tool.
Process Summary Notes:
Part 1, Step 2: Explain how you set up your SoilErase model.
1. First, open a new ArcMap .mxd, and add the shapefiles soils and basin.
2. To create a model, open ArcCatalog, right-click the folder in which you are working (ex. Module5), select New, and then Toolbox.
3. Rename the toolbox appropriately, then right-click it, select New, and then Model.
4. This will cause a ModelBuilder window to open. In the top menu, select Model¸ then Save As, then name the model.
5. For this model, the task is to clip the Soils shapefile to the extent of the Basin shapefile, then remove the features within Soils that have the attribute “Not prime farmland.”
6. From the ToC on the .mxd, click and drag both Soils and Basin shapefiles into the ModelBuilder window. These will be the inputs, and they will show up as blue oval boxes, with the names of the shapefiles inside.
7. The Clip and Select tools are dragged from the ArcToolbox > Analysis Tools > Extract toolset, into the ModelBuilder space. They will show up as yellow, rectangular boxes.
8. The Connect tool is used to draw arrows from the input shapefiles, to the tools. Although Select or Clip can done in either order, I did Clip first.
9. As I drew the arrow from Soils to Clip tool, a box appeared, in which either input feature or clip feature could be indicated. Because the Soils is being clipped, it is the input feature.
10. Then, another arrow is drawn from Basin to Clip, and in this case, the clip feature option is selected.
11. After this is done, a new box appears for the output, supplied with a default name. This box is a green oval, indicating that it is an output.
12. The Select tool box is set to the right of the new output from the clip tool, and an arrow is drawn from the clip output, to the select tool box. Parameters must be set; this can be done by double-clicking the Select box. In the SQL dialog, enter, “FARMLNDCL” = ‘Not prime farmland”
13. A new output box (green oval) appears, which contains the selected features from the last output.
14. The Erase tool is dragged into the ModelBuilder, and an arrow is drawn from the last (Select) output box, to the Erase tool box. The input feature is the clipped soil shapefile, and the Erase feature should be the Selection of the last output (those tracts that are Not prime farmland.)
15. The new output feature, and the final one, is the soil tracts that fall within the extent of the basin, with those of attribute “Not prime farmland” removed.
16. After this is done, right click the final output, after the Erase tool, and select “Add to Display.”
17. On each of the 2 inputs (blue ovals) and 3 outputs (green ovals), right-click, and check “Model Parameter.” A “P” will appear next to each of those boxes. (This is not done to the tools.) This will make it possible to change the input features in the model, as well as the file paths, and make the model useful for general purposes.
18. From the top menu: Model > Save.
You are also strongly encouraged to include any other notes you have on this week’s lecture and lab or your process.
(These extra notes are optional, and are not required for any part of your grade. However, they can greatly improve your learning experience by reinforcing what you’ve learned, and giving you a reference to look back on in the future. Plus, they can make your blog posts more interesting!)
Other notes:
1. After model is exported to Python script form, you must
2. add the “import arcpy” line of code at the top, and then
3. arcpy.env.overwriteOutput=True
4. you must also make sure each shapefile’s entire file path is specified for the variables.
This problem exists for the Select tool, when it is used from within the ModelBuilder: the attribute in the soils shapefile is "Not prime farmlands," with the p and f in lower case. However, when you enter that into the SQL statement, inside ModelBuilder, either by typing it in, or selecting it from the "Get Unique Values," it always reverts to "Not Prime Farmland," with capital P and F, even if you change it back to lower case and save it. This is not the correct name for the attribute, so nothing is selected. I've included a screen shot.
I tried running this process manually, using the Clip, Select and Erase tools separately, directly from the toolbox. In this case, the problem DID NOT happen. The p and f in Not prime farmland did NOT revert to caps, the selection was created, and it was properly erased from the soils shapefile.
took out the quotes, put em back in again, erased the whole statement and added it in again, and now the select works and the Not prime farmlands gets properly erased!
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