Compute local scales in meters per degree, for use with WGS84 geocoordinates.

local_scales.js

const turf = require("@turf/turf")

const points = {
    "Bertilsvägen 7, containern": [17.583636, 59.855249],
    "Granskogen": [17.570114, 59.864838],
    "Skäggesta, korsningen": [17.552488, 59.872742],
    "Hågahögen": [17.586869, 59.837368]
}

// A small value for the finite difference derivative approximation.
const eps = 0.001;

// Turf.js gives distances in kilometers, but I want meters
const metersPerKilometer = 1000; 

Object.entries(points).forEach(([label, [lng, lat]]) => {
    const distanceEW = turf.distance(
        turf.point([lng, lat]),
        turf.point([lng + eps, lat])
    ) * metersPerKilometer;

    const distanceNS = turf.distance(
        turf.point([lng, lat]),
        turf.point([lng, lat + eps])
    ) * metersPerKilometer;

    // Local derivative approximations by finite difference.
    // Meters per degree longitude and latitude, respectively.
    const localScales = {
        EW: distanceEW / eps,
        NS: distanceNS / eps,
    };
    console.log(label, localScales);   
})