Dynamically Scaled Buffers and Distance — J.K. Berry calls em “rubber rulers”
Vector thinking…..What if the size of a buffer is not everywhere the same? Perhaps because the underlying reason for the buffer varies. The size of a riparian forest buffers would depend on the size of the stream, larger buffers for larger streams if the goal is to mitigate flooding. Here we create a variable called “buffer” in the river attribute table that is used to “scale” the buffer as it is applied to different segments. You can apply this dynamic buffer using the “Data Defined” dropdown menu next to Distance, and selecting the field from the attribute table you stored the dynamic buffer values for each stream. Where these buffers overlap, you can check the “Dissolve result” option. You ccan see the reuslts i yellow for our Dutch stream from earlier.
In 2020, Virginia implemented a new GIS based system to identify high priority conservation land, based on several conservation goals (https://www.dcr.virginia.gov/conservevirginia/). For water quality, they first sought to “ identify watersheds (12-digit hydrologic units) with the highest (i.e., those in the 90th percentile) loadings of nitrogen, phosphorous, or sediment from any of the assessments used.” And then created stream buffers, dynamically scaled to slope. “Buffers were mapped for these waterways, where buffers ranged from 100 to 400 ft., depending on steepness of slope of adjacent lands. ” source How’d the do that?? We can explore these dynamic buffers on Virginia’s Natural Heritage Data Explorer
Grid thinking…….We can also do buffer size based on land use. Here I have…
1. simplified a landuse maps to five categories (buildg)
2. made a distance to stream map (clipped-stream-dist-expanded), then
3. used these two maps to select areas within given distances from the stream depending on the landuse (Raster Calculator)
Areas of study area more than 50 m from stream, but near a house, highlighted in green
("buildg@1" = 1) AND ("clipped-stream-dist-expanded" > 50)
Further thinking….
Q: How would the shape of this buffer change if we iterated over multiple land use categories?
Q: How about in vector world? How would you do the same thing