Google Earth Engine: Accessing image properties inside .map() function

Google Earth Engine: Peeking Inside Images While Mapping – A Real-World Guide

Google Earth Engine (GEE) – it’s a powerhouse, right? I mean, where else can you play with petabytes of satellite imagery without melting your laptop? One of the things you’ll find yourself doing constantly is looping through collections of images, doing something cool to each one. That’s where the .map() function comes in. But here’s the thing: sometimes you need to grab a piece of information from the image itself – its acquisition date, maybe the cloud cover percentage, or even just which satellite took the picture. That’s where things can get a little… well, let’s just say it’s not always obvious how to do it. So, let’s break down how to actually access those image properties from inside a .map() function.

.map(): Your Looping Sidekick

Think of .map() as your trusty sidekick for image collections. You give it a function, and it diligently applies that function to every single image in your collection. Simple as that. The basic idea looks like this:

collection.map(function)

Collection is your stack of images (or features, for that matter), and function is the task you want to perform on each one. The function takes one image at a time, works its magic, and spits out either a modified image or something totally new.

The Head-Scratcher: Getting at Image Info

Here’s where many folks, myself included at first, get tripped up. You can’t just wave your hand and expect to grab the image’s properties like they’re floating in the breeze. GEE runs this .map() stuff on Google’s servers, not on your local machine. So, you have to explicitly tell GEE to fetch that property information and pass it to your function. Think of it like ordering room service – you have to pick up the phone and ask!

Solution #1: image.get() – Your Room Service Key

The easiest way to grab a property is with the image.get() method. It’s like saying, “Hey GEE, give me the value of this specific property from this image.” Check this out:

javascript