Methodologies

Average Street Shade per Segment Methodology

Layers needed

  1. City Limits (polygon)
  2. Streets (line)
  3. Canopy (polygon)

Steps

  1. Buffer the Streets layer to 20ft each. Be sure to use flat buffers in this step. This creates segments that have less overlap at intersections than if round buffers were used. The types of buffers used are displayed below.
  2. Clip the canopy layer to the streets buffer layer. You will now have the canopy that is only inside the streets. The image below shows the clip function loaded with the tree canopy in the input feature and the street buffered layer as the clip feature.
  3. Calculate the area of each street segment. Open your buffer (street buffer) attribute table. Create a new field in the attribute table titled shape_area and make sure to choose double for the “type”. Populate the newly created field by using the calculate geometry function. Select area as the calculation and click ok. We used square feet as the area measurement.
  4. Dissolve the canopy layer created in Step 2. Make sure to select the “create multi-part” feature on the bottom of the dissolve window. This creates a multi-parts part polygon.
  5. Create new field in the dissolved layer and use “calculate geometry” to calculate the area of the multipart polygon. This creates a unique field that will be used to identify polygons in the next step
  6. Preform a union using the streets buffer and dissolved canopy layer.
  7. Open the attribute table of the new union layer and delete the polygon features that contain the same value as the dissolved polygon area in field made in Step 5. This eliminates the canopy polygons leaving only the areas without shade.
  8. Create a new field within the union result layer table and use calculate geometry (area). This newly calculated field represents the area without shade, per segment.
  9. Perform a spatial join between the original street buffer layer and the union layer mentioned in the step 7. When preforming the join choose “within’ under the match option category, and set the street buffer layer as the target feature and the union layer as the join feature.
  10. Create a new field in the street buffer layer and use field calculator to subtract the area with no shade from the buffered area. This gives us field populated with the area of shade within each street.
  11. Create a new field in the street buffer layer that will contain the shade percent. To populate the field use the field calculator and divide the shaded area field by the buffered area field then multiply your result by 100 to get a percentage
  12. Perform one last spatial join to display the shade indices as lines so that we can adjust the line thickness for visual purposes. To do this perform a spatial join with the original streets layer as the target feature and the buffer layer as the join feature. This function will copy over the attribute table and associated values to the line files.
  13. To further the visual representation of the final layer we will assign a graduated color scheme to it. We will assign it to 4 equal intervals with a sampling size of 100,000. 

 

Average Street Shade Percent for Neighborhoods

Layers needed

  1. City Limits (polygon)
  2. Streets (line)
  3. Neighborhoods (polygon)
  4. Canopy (polygon)

Steps

  1. Buffer the streets – Use 20ft buffers. Make the buffers full with flat ends (opposed to round ends).
  2. Clip the neighborhoods to the city limits
  3. Clip the buffered streets to the new neighborhoods
  4. Clip the canopy layer to the street buffer layer
    1. You should now have the street buffers within neighborhoods within city limits and canopy In street buffers within neighborhoods within city limits
  5. Dissolve street buffers layer
  6. Dissolve Canopy in streets layer
  7. Union the dissolved canopy layer and neighborhoods layer (uncheck “gaps” box)
    1. Open attribute table of new union layer and delete -1s in the FID (layername) field
  8. Union the dissolved streets buffer layer and neighborhoods layer (uncheck “gaps” box)
    1. Open attribute table of new union layer and delete -1s in the FID (layername) field
  9. Add new field to canopy union layer. Calculate area using the calculate geometry function
  10. Add new field to street union layer. Calculate are using the calculate geometry function
  11. Table Join the canopy neighborhood union layer to the neighborhoods clipped to city limits layer using a unique ID (we used GIS ID)
  12. Table Join the streets neighborhood union layer to the neighborhoods clipped to city limits layer using a unique ID (we used GIS ID)
    1. Now the data from the two union layers will be included in the neighborhood polygon layer attribute table
  13. Create a new field in the neighborhood layer. This field will be used to calculate the percent shade. Populate the field using field calculator with the formula canopy area/street area X 100

 

Average Street Shade Percent per Watersheds

Layers needed

  1. City Limits (polygon)
  2. Streets (line)
  3. Watershed (polygon)
  4. Canopy (polygon)

Steps

  1. Buffer the streets – Use 20ft buffers. Make the buffers full with flat ends (opposed to round ends).
  2. Clip the watersheds to the city limits
  3. Clip the buffered streets to the new watersheds
  4. Clip the canopy layer to the street buffer layer
    1. You should now have the street buffers within watersheds within city limits and canopy In street buffers within watersheds within city limits
  5. Dissolve street buffers layer
  6. Dissolve Canopy in streets layer
  7. Union the dissolved canopy layer and watersheds layer (uncheck “gaps” box)
    1. Open attribute table of new union layer and delete -1s in the FID(layername) field
  8. Union the dissolved streets buffer layer and watersheds layer (uncheck “gaps” box)
    1. Open attribute table of new union layer and delete -1s in the FID(layername) field
  9. Add new field to canopy union layer. Calculate area using the calculate geometry function
  10. Add new field to street union layer. Calculate are using the calculate geometry function
  11. Table Join the canopy watershed union layer to the watersheds clipped to city limits layer using a unique ID (we used GIS ID)
  12. Table Join the streets watershed union layer to the watersheds clipped to city limits layer using a unique ID (we used GIS ID)
    1. Now the data from the two union layers will be included in the watersheds polygon layer attribute table
  13. Create a new field in the watersheds layer. This field will be used to calculate the percent shade. Populate the field using field calculator with the formula canopy area/street area X 100
    1. If the field calculator has an error calculating null values, export the layer (this will turn null values to 0).
    2. If the calculator has an error calculating values of 0, select only the values that are not zero and run field calculator function.