on December 28, 2022

A way to identify which ui.Map() instance a widget is located in Earth Engine

Hiking & Activities

Figuring Out Which Map a Widget Belongs To in Earth Engine: A Real-World Guide

Ever built a Google Earth Engine app with multiple maps and found yourself scratching your head, wondering how to connect a button to the right map? Yeah, been there! It’s a common head-scratcher: how do you tell which ui.Map() instance a particular widget—be it a button, slider, or whatever—is hanging out in? Knowing this is key to making your app behave, ensuring clicks and tweaks affect the map you intend them to. So, let’s dive into how to solve this little puzzle.

Think of Earth Engine’s UI like a set of nested building blocks. You’ve got widgets, which are those interactive bits and bobs, and they all live somewhere, usually starting with the ui.root panel, which is like the main stage. The default map you see in the Code Editor? That’s a ui.Map object. But the cool thing is, you can create more maps and stick them in panels or directly onto that main stage.

Okay, so how do we actually figure out which map a widget calls home? Here are a few tricks I’ve picked up:

  • Pass the Map Like a Baton: This is the cleanest way, especially when you’re building widgets inside functions. Just pass the ui.Map() instance as an argument. This way, the widget’s callback function knows exactly which map to mess with.

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