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. Activate the 2nd map frame in the buffers project.
Note how the buffer size changes in relation to the table value.
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’ve
1. simplified a landuse maps to just four categories (Gen_Use)
2. made a distance to stream map, then
3. used these two maps to select areas within given distances from the stream depending on the landuse
(Using raster calculator).
("gen_use" == 1) & ( "dist2stream" < 400) | ("gen_use" == 2) & ( "dist2stream" < 200) | ("gen_use" == 4) & ( "dist2stream" < 100)
Aside: Moving to WordPress caused a frustratingly minute change that resulted in failure of the equation above when it was pasted into the Raster Calculator. WordPress had changed the “straight” double quotes to “curly” double quotes (what Microsoft Word calls “smart” quotes).
The top line was copied from my old html page and the bottom was how WordPress rendered it. The straight quotes (the inch symbol) are in basic ASCII tables (ASCII code #34) and are recognized by the Python interpreter in ArcGIS Pro as defining layer names, but the curly ones (#8220 and ”, left and right respectively) are not. Another hour of my life down the rabbit hole…..
Back to GIS: Note how the buffer changes size depending on the landuse category, but also note how there are pieces of buffer isolated from others because of localized changes in land use parallel to the stream. (north of the words KERRS CR)
How about in vector world? How would you do the same thing?