In Part II, we will use the roads dataset to create raster data layers of habitat quality and forest patches. In Part III, we will generate statistics about the size, shape, and habitat quality of each forest patch.
We will use the following coded values:
When you convert a feature layer to a raster, you have to choose a field in the feature layer from which to base the grid cell values on. You often need to create a new dummy field and assign a value that is consistent for all of the records you want to convert (like we did above).
It is also important to note that if there are any selected records in the vector layer, only those records will be converted to a raster layer. Therefore, be sure to clear any selected features before performing the conversion.
The data type of the field you choose is very important. For example, if you choose a numerical field that contains decimal values, the resultant grid will not have an attribute table. However, if you choose an integer field, the resultant raster will have an attribute table. If you choose a text field, ArcGIS will automatically assign each unique text value an integer code in a new field named "VALUE."
The new raster layer will be created based on all defined Spatial Analyst environment settings. Always check these settings before converting features to a raster to avoid potentially undesirable results.
It is important to note that although the extent setting is utilized by Feature to Raster, the mask setting is ignored. Although you will not notice this with the "RoadsGrid.tif" layer, you will see the effects of this when you create a buffered grid later in this lesson.
Make sure you have the correct answer before moving on to the next step.
The "RoadsGrid.tif" raster should have the following information. If your data does not match this, go back and redo the previous step.
Remember from the Background Information section that edge effects can occur up to 2 km from roads. We will consider all areas 2 km from roads as "edge habitat" and areas farther than 2 km from roads as "interior habitat." To do this, we need to create a buffer of the road centerlines.
Make sure you have the correct answer before moving on to the next step.
The "EdgeGrid" raster should have the following information. If your data does not match this, go back and redo the previous step.
Did the Reclassify Tool honor the mask and extent settings?
Hint: Compare the InteriorGrid.tif and EdgeGrid.tif rasters along the study area boundary.
Make sure you have the correct answer before moving on to the next step.
The "InteriorGrid.tif" grid should have the following information. If your data does not match this, go back and redo the previous step.
In steps 1, 2, and 3, we created three individual grids, one for each level of habitat quality. To continue the analysis, we need a way to merge all of the data sets into one grid. The Mosaic to New Raster tool in Toolboxes will allow you to mosaic multiple raster data layers together by stacking them on top of one another. The values in the output raster will be determined based on the order the files are specified during the mosaic. Cells will first be assigned according to the cell values in the first input raster; all remaining null values will be filled in with the middle input raster, and so on. We want the roads to be on top of the stack, the edge habitat in the middle, and the forests on the bottom.
This tool does not honor the Output extent environment settings. If you want a specific extent for your output raster, consider using the Clip tool. You can either clip the input rasters prior to using this tool, or clip the output of this tool.
Make sure you have the correct answer before moving on to the next step.
The "HabMosaic" raster should have the following information. If your data does not match this, go back and redo the previous step.
What value was assigned to areas with roads, since they have data in both the "RoadsGrid" and "EdgeGrid" rasters?
Which habitat type (roads, edge, or interior) covers the majority of the study area?
How can you calculate the area of each habitat type?
The Raster Calculator utilizes all raster environment settings, so it is highly useful when working with raster data. As displayed above, simply selecting a raster layer and running the Raster Calculator will generate a new raster layer based on the current environmental settings. Try changing these settings to see the differences when running the Raster Calculator on a particular raster layer.
Make sure you have the correct answer before moving on to the next step.
The "HabitatGrid" raster should have the following information. If your data does not match this, go back and redo the previous step.
We now have one grid with values showing the range of habitat quality within the study area. The next step is to create a grid of forested areas, which we need to create the forest fragments. We will use the "RoadsGrid.tif" raster we created in Part II Step 1 to create a new grid representing forested areas (cells that are NOT roads).
Make sure you have the correct answer before moving on to the next step.
The "ForestGrid.tif" raster should have the following information. If your data does not match this, go back and redo the previous step. You may need to adjust for the Mask and Processing Extent here as well.
Make sure you have the correct answer before moving on to the next step.
The "ForestPatches.tif" grid should have the following information. If your data does not match this, go back and redo the previous step.
OID | Value | Count | link |
---|---|---|---|
0 | 1 | 64201 | 1 |
1 | 2 | 58 | 1 |
2 | 3 | 122867 | 1 |
3 | 4 | 19 | 1 |
4 | 5 | 30 | 1 |
Why did we use the number "100" to calculate the area?
Make sure you have the correct answer before moving on to the next step.
The "ForestPatches.tif" grid should have the following information. If your data does not match this, go back and redo the previous step.
oid | value | count | forestid | area_sq |
---|---|---|---|---|
0 | 1 | 64201 | 1 | 642010000 |
1 | 2 | 58 | 2 | 580000 |
2 | 3 | 122867 | 3 | 1228670000 |
3 | 4 | 19 | 4 | 190000 |
4 | 5 | 30 | 5 | 300000 |
5 | 6 | 1 | 6 | 10000 |
6 | 7 | 13 | 7 | 130000 |
7 | 8 | 1 | 8 | 10000 |
8 | 9 | 318427 | 9 | 3184270000 |
How many individual forest patches are there? Which forest patch is the largest? Which forest patch is the smallest? Why do you think there are so many patches with an area of exactly 10,000 sq m?