How do I only use the top layer or feature clicked on a multilayer OpenLayers3 map?

Taming Click Events: Grabbing Just the Top Feature on Your OpenLayers 3 Map

OpenLayers 3? It’s a seriously cool JavaScript library for whipping up interactive web maps. And if you’re building anything beyond a basic map, you’ll probably run into this: handling clicks to select features. Now, when you’ve got multiple layers stacked on top of each other, things get tricky. You want to make sure you’re only messing with the feature that’s actually on top, the one the user intended to click, and not accidentally triggering actions on stuff underneath. So, how do you do it? Let’s dive in.

The Multilayer Map Conundrum

Imagine this: you’ve got a map showing cities and roads. The cities are little dots, and the roads are lines. Sometimes, a city dot sits right on top of a road line. When a user clicks, you want to select the city, not the road underneath. That’s the challenge we’re tackling. A simple click event can fire off actions on everything at that spot, leading to chaos. We want precision.

The Secret Sauce: Targeting the Topmost Feature

OpenLayers 3 gives us a few ways to figure out what’s at a specific spot on the map. The trick is using them smartly to grab only what we want.

1. forEachFeatureAtPixel: Your Go-To Tool

Think of forEachFeatureAtPixel as your detective. It checks every feature at a given pixel and lets you do something with each one. Here’s the basic setup:

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