Longitude is the angular coordinate for an east–west position, measured from the Greenwich meridian. It pairs with latitude, which measures north–south position. section 13.1.1
In a D3 map, longitude is supplied with latitude to a projection, which converts the geographic pair into an x–y position inside an SVG container. section 13.2.4 section 13.7
Plotting a city
A city record can store latitude and longitude alongside its name and related data. Passing [longitude, latitude] to an Equal Earth projection returns the coordinates used to position its SVG circle. section 13.2.4
const projection = d3.geoEqualEarth(); [x, y] = projection([longitude, latitude]);
Use the projection call to transform a geographic coordinate pair into drawable [x, y] coordinates. section 13.7
