Skip to content

Instantly share code, notes, and snippets.

@clhenrick
Last active January 11, 2024 12:33
Show Gist options
  • Save clhenrick/5787a12a8bf3b02821839e4f9556d997 to your computer and use it in GitHub Desktop.
Save clhenrick/5787a12a8bf3b02821839e4f9556d997 to your computer and use it in GitHub Desktop.
Node.JS script to aggregate NYC vehicle collision data into a hexagonal grid and compute the ck means for each cell using Turf.JS and Simple Statistics.JS
node_modules/
.DS_Store
// load libraries
const fs = require("fs")
const turf = require("turf")
const turfMeta = require("@turf/meta")
const simpleStats = require("simple-statistics")
const d3 = require("d3-array")
// load our data
const data = require("./nyc_crashes.json")
// rough geographic bounding box of NYC
const bbox = [ -74.24939, 40.50394, -73.701195, 40.90995 ]
// size in kilometers we want each side of our hex grids
const cellSize = 0.5
// create the hexbin geometry for the given bbox and cell resolution
const hexGrid = turf.hexGrid(bbox, cellSize)
// perform a "spatial join" on our hexGrid geometry and our crashes point data
const collected = turf.collect(hexGrid, data, "cartodb_id", "values")
// get rid of polygons with no joined data, to reduce our final output file size
collected.features = collected.features.filter(d => d.properties.values.length)
// count the number of crashes per hexbin
turfMeta.propEach(collected, props => {
props.count = props.values.reduce((acc, cur) => acc += 1, 0)
})
// reduce our count values to a new array of numbers
const reduced = turfMeta.featureReduce(collected, (acc, cur) => {
acc.push(cur.properties.count)
return acc
}, [])
// compute the ckMeans binning for data into 7 classes from reduced values
const ck = simpleStats.ckmeans(reduced, 7)
// tack on the bin number to our data, as well as its min and max values
turfMeta.propEach(collected, props => {
ck.forEach((bin, index) => {
if (bin.indexOf(props.count) > -1) {
props.bin = index
props.binVal = d3.extent(bin)
}
})
})
// remove the "values" property from our hexBins as it's no longer needed
turfMeta.propEach(collected, props => {
delete props.values
})
// write output data
fs.writeFileSync("./processed.json", JSON.stringify(collected))
Display the source blob
Display the rendered blob
Raw
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
View raw

(Sorry about that, but we can’t show files that are this big right now.)

View raw

(Sorry about that, but we can’t show files that are this big right now.)

View raw

(Sorry about that, but we can’t show files that are this big right now.)

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment