Learn D3.js

Lines and outlines

You can add any parallels or meridians to a map by filtering graticule lines with step() and extent(). The following illustration shows the code used to create a detailed area within a larger map, and standard parallels for the tropics and polar circles.

Standard parallels and areas with different graticules density can be configured using step and extent configuration. Code: Circles/5-graticules-step.html and 7-graticules-tropics.html.

Instead of circles, you can also draw lines and polygons on a map using simple GeoJSON geometries. Another way to draw the equator is to pass a LineString as the datum:

const equator = {type:"LineString",coordinates:[[-179.9,0],[0,0],[179.9,0]]} ...