Detect Change - Where the Ground Changed Between Two Years

The Detect Change kit shows you where the ground changed on a site between two years, so you know where to look before you drive out. It finds new buildings, cleared land, fires, floods and new development anywhere on Earth.

• Preview: a free change layer over the whole map while you pan, to spot the busy areas.
• Change map: pick a site and get a 10 m change map with numbered hot spots, largest change first.
• Before and after: click a hot spot to see a picture from each year, with a slider to compare them.

Who can use it

Detect Change is a Pro Business kit. Every signed-in account also gets 3 free change detections to try it, and the preview is free for every signed-in account. A run that fails, or a site with no data in both years (open water, for example), does not use a free run. Looking at hot spot pictures does not use one either, but without Pro Business you need to make a run first.

A site can be up to 25,000 acres (about 100 square kilometres).

Add the kit

1. Open Maps & Data and go to the Kits tab.
2. Find Detect Change and click Use Kit.

You can also right-click a polygon, rectangle or circle on your map and choose Detect change. The kit opens with that shape as the site.

Pick the years

Choose a Baseline year (the earlier one) and a Comparison year (the later one). Any two different years from 2017 to the latest year work. The kit starts with the oldest and the newest year.

The free preview

Click Show change preview to add the change layer to the map. Zoom in to a city or closer to see it. The brightest areas changed the most. Use Preview opacity to see the map under it.

The preview is coarser (40 m) than a change map, and it is not saved with your map. Click Hide change preview to turn it off. If the day's preview budget is used up, the kit says so. It resets at midnight UTC.

Make a change map

1. Click Use selected shape to pick an area on your map, or Draw site to outline one. Click the first point to finish.
2. Click Create layer. Large sites can take up to a minute.

The change map goes on your map in a Detect Change folder, with:

• The change layer: each 10 m square colored by how much it changed. No change is clear, and low, moderate, high and very high change go from pale yellow to red.
• Hot spots: purple outlines around areas of strong change. The 10 largest are numbered, from the largest change down.
• A report card next to the site: the site's area, the area that changed, its share of the site, the color legend and the hot spot list.

Look at a hot spot

Click a hot spot in the kit's list. The map zooms to it and the kit loads a picture from each year. Drag the slider to swipe between before and after. The caption under each picture shows its date and source: a Sentinel-2 satellite picture (10 m), or in the US a NAIP aerial photo when NAIP has both years.

• Add pictures to map puts both pictures on your map in a folder for that hot spot.
• Order high-res imagery opens imagery ordering if you need a sharper look.

If a year has no clear picture, the kit says so.

How to read it

The change comes from Google's AlphaEarth Foundations satellite embeddings: a yearly summary of many satellite sources for every 10 m square on Earth. Because it uses more than photos, it can also catch change that is hard to see in a picture, such as wetter ground or more plant growth.

It is a yearly satellite measure, not a survey or a legal record. Check a hot spot in the pictures, or in person, before you act on it.

Where the data comes from

• Change: the AlphaEarth Foundations Satellite Embedding dataset, produced by Google and Google DeepMind (CC BY 4.0), read from AWS Open Data.
• Pictures: Copernicus Sentinel-2 satellite data, and NAIP aerial photos for some US sites. Each picture's credit shows under it.

Ask Scribble

You can ask Scribble to do it for you, for example:

• "What changed on this site between 2018 and 2024?"
• "Find new construction here since 2019."
• "Show me the before and after of the biggest hot spot."
• "Turn on the change preview."