Last updated May 24, 2019

Mapbox bounds

This week we had a request with a quick turnaround for our marketing team. We needed to stand up a static site with a specific Mapbox. The data layers were all set up, we just needed to host it somewhere (to eventually be embedded in an iframe elsewhere).

The problem

We only had a small segment of layers to use, so outside those bounds was just darkness. We weren’t provided with any bounding information, so we had to figure it out on our own.

The solution

Adding bounds to a Mapbox instance is mostly a matter of configuration. You provide the bounding coordinates as an array, with the Southwest coordinates in the 0 position, and the Northeast coordinates in the 1 position. Then you pass it to the maxBounds property on the mapboxgl.Map() object.

var bounds = [
    [xx.xx, xx.xx], // Southwest
    [xx.xx, xx.xx]  // Northeast
];

const map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/yourstylehere',
    center: [xx.xx, xx.xx],
    zoom: 16.0,
    maxBounds: bounds
});

But if you don’t have those bounding coordinates available at the outset, you’ll need to find them yourself. We wrote a quick function to alert() us with the coordinates of any clicked point. It looks like this:

map.on('click', function (e) {
    alert(JSON.stringify(e.lngLat));
})

With this function added to the Mapbox JavaScript, we were able to eyeball the points we wanted to use as bounds, click the map, and copy-paste the values. Problem solved.

Limitations

Don’t leave it in your production code!

You probably don’t want to leave your click handler in production code (unless you’d like end-users to be able to grab coordinates as well). So I think it’d be a little more satisfying to set up the function behind some environment variable, and maybe even a hidden trigger.

In my mind, it would be cool to add something like: enableCoordinateGrabber() to the code. If you were to enter that in console, JavaScript would register the click handler, and you could dismiss it with disableCoordinateGrabber() or something.

Eyeballing the coordinates

Because of the time frame and use case, we didn’t select very precise bounds. We just eyeballed what we thought would be good, and that required a bit of guess-and-check. I’m sure there’s a more optimal way to calculate appropriate bounds for a given area of interest.