Chlorosat

About Chlorosat

Chlorosat shows how green the land is, anywhere on Earth, on a 3D globe of satellite photos. Pick one year from 2019 to 2026, then zoom in on any place to look closer. Chlorosat does not yet compare two years or calculate regional statistics.

What the colors mean

The colors come from NDVI (Normalized Difference Vegetation Index). Healthy leaves reflect a lot of near-infrared light, which our eyes can't see, and absorb red light. Satellites measure both, and NDVI turns the difference into one number. Dark green means dense, healthy vegetation such as forest, green healthy plants, yellow sparse or dry vegetation, and red little or none: bare ground, rock, roads and buildings.

Water is left clear so you can see the photo. Sometimes NASA has no reading at all for a spot. On land, those gaps are shown as red, the same as "no vegetation", because they are almost always dense city centers. Midtown and Lower Manhattan are a permanent gap in NASA's data, for example. On a few very small islands this can make a green island look red.

Using the map

  • Year: slide to pick a year from 2019 to 2026. The map loads it once you stop sliding, and the satellite photos change to that year too.
  • Opacity: fade the vegetation colors to see the photo underneath, or hide them with the eye button.
  • Satellite / Map: switch between satellite photos and a plain street map.
  • Moving around: drag to spin the globe, scroll or pinch to zoom. The + and − buttons zoom too (on phones, pinch instead).
  • Compass: if the globe gets turned or tilted (a two-finger twist on a phone), a compass appears above the reset button. Its red tip points north; press it to turn north back to the top.
  • Reset: the circular-arrow button flies back to the whole globe.
  • Find my location: the target button flies to where you are and marks it with a blue dot. The light-blue circle around it shows how sure your device is. Laptops without GPS often only know roughly where they are; then the circle is large, the map shows the whole area you could be in, and it keeps improving for a few seconds if a better fix arrives.
  • On a phone: Year and opacity are in the ☰ menu in the search bar, and tapping the ⓘ credit line at the bottom shows the full credits.

Searching

  • Type a city, country, park, landmark or address and pick a result, or just press Enter for the top one. The map frames the whole place: a city fills the screen, a continent shows the whole globe.
  • When you're zoomed in on an area, places nearby come first: searching "Target" while looking at Norman finds the Norman store, while famous places still win ("Paris" is still France).
  • Common names work as well as official ones: "Ivory Coast", "Czech Republic" or "Burma" find the right country.
  • Clicking the empty search box shows your last 10 searches. Picking one goes straight there without searching again.

Your privacy

There are no accounts and nothing to sign in to. Your recent searches are saved only in your own browser, and you can remove them one by one or clear them all. Your location is only used in your browser to move the map; Chlorosat doesn't send it anywhere or store it. What you type in the search box is sent to Photon, the search service, to find places.

Where the data comes from

  • Vegetation (NDVI): NASA's MODIS sensor on the Terra satellite, through NASA GIBS. Each year shows the mid-August 16-day average.
  • Satellite photos: Esri World Imagery (Maxar, Earthstar Geographics and others). Each year uses Esri's archived imagery from about that August, and the credit line at the bottom shows when the photos on screen were actually taken.
  • Place names, borders, water outlines and the street map: OpenStreetMap contributors, through OpenFreeMap and OpenMapTiles.
  • Place search: Photon by komoot, built on OpenStreetMap.

Good to know

  • Detail: each NASA measurement covers about 250 m by 250 m, roughly a few city blocks. Zoomed in close, the colors are that measurement enlarged and blended smoothly; they can't show a single yard, field edge or tree.
  • Season: mid-August is the peak of the growing season in the Northern Hemisphere but winter in the Southern Hemisphere, so places like Australia, Argentina and South Africa look less green than they do in their own summer.
  • Greenness, not causes: NDVI shows how much healthy leaf there is. It can't tell you why an area changed (drought, a fire, a harvest, new buildings), only that it did.
  • Photos: the satellite photos are stitched together from many pictures taken on different days, so you may see seams where two meet, or clouds and shadows in places.

Chlorosat is Group E's CS 3203 project (Adam, Carter, David, Kevin and Lucas). Next, it will also map vegetation with visible light (a normal color photo) next to NDVI, and explain why the two can differ, for policymakers, environmental groups, scientists and homebuyers.