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Online forest mapping made easy

Penas Blancas Forest, Costa Rica. Photo credit: George Powell

Penas Blancas Forest, Costa Rica. Photo credit: George Powell

  • The online Global Forest Watch platform provides open access to frequently updated satellite imagery to allow any user to monitor forest change in a given country or other area.
  • Within an interactive map, the user can view forest change data and related spatial data sets at scales ranging from a 30m x 30m pixel to the whole globe – basic user guidelines provided in this post.
  • Speeding detection of forest loss improves management, conservation, and accountability.

As human development expands across the globe, forest loss in remote areas, including protected areas, often goes undetected until large areas have been cleared. Greater transparency to reveal the condition of forest habitat at high spatial resolution is increasingly central to not only halting forest loss directly, but also planning effective conservation strategies for forest-dependent species.

To speed detection of forest loss and provide greater transparency of forestry practices, several initiatives are enabling online forest monitoring. The most easily available of these is Global Forest Watch (GFW), a free online forest monitoring and analysis tool the World Resources Institute (WRI), Google, ESRI and the University of Maryland launched in 2014.

Given its open access and global reach, we believe a consolidated basic summary-in a series of articles-would benefit readers interested in using the tool. The GFW site itself provides an extensive set of user-friendly guides and tutorials.

Slash and burn agriculture in Aceh, Indonesia
Slash and burn agriculture, like this in Aceh, Indonesia, gradually eliminates forest across the tropics. Photo credit: Rhett A. Butler

What it does

The Global Forest Watch (GFW) online platform compiles and uses satellite imagery, other spatial data sets and related algorithms to identify where trees are growing and disappearing. GFW applies this information to display up-to-date global tree cover and detect forest loss and gain worldwide. GFW updates its global map of tree cover* annually (from 2000 to 2014) at 30m x 30m resolution and bi-weekly at 500m resolution. The platform aims to provide open access to timely information aiding forest management and conservation worldwide.

How people use it

The tool is free, so anyone with internet can access the information on forest cover, loss and gain at a variety of scales.  Its creators want different sectors to take from GFW what they need to inform their work. Thus,

In fact, uses the tool regularly to add maps to stories on deforestation and other destructive land uses.

To introduce this powerful tool, this post highlights several basic “where to’s” and “how to’s,” including links to related instructional materials on the GFW website.

The GFW Interactive Map with a satellite imagery base for central Africa
The GFW Interactive Map with a satellite imagery base for central Africa. Image credit: GFW

1) How to view tree cover, loss and gain worldwide and in your selected area

On the GFW website homepage, scroll down and click on the icon for the Interactive Map. This is where you can view all forest change and related data layers in one place.  This main page highlights the world’s forests and areas of forest loss (in pink) and gain (in blue) at 30m resolution.

GFW welcome screen-interactive map
The GFW welcome screen with an introduction to the Interactive Map. Image credit: GFW

The interactive map initially offers step-by-step instructions on its various features, and you can revisit each of these in a tutorial.

The instructions highlight the (1) tabs at the top of the screen containing different categories of data you can add to your map; (2) data legend at the left displaying the different data layers already on your map; and (3) navigation features to zoom in to see the information in better detail or zoom to a particular location in the world.

To add data layers to overlay with the forest change data, click on the category tabs at the top of the map.

Each tab brings up a menu of additional global data sets—including forest cover, land use, mangrove forests, fires occurring over the past day or week, dams, protected areas and human population density—to appear with the layers showing global tree cover loss and gain.

You access data layers from tabs at the top of the Interactive Map. Image credit: GFW
Tabs at the top of the Interactive Map provide access to the data layers. Image credit: GFW

You can also overlay data sets specific to certain countries, including tree and palm oil plantations, mining concessions, logging roads and land use rights.

A box at the right of the map presents a menu of environments with four icons, where you can:

GFW right menu box of interactive map
The Interactive Map’s menu box with options to view by country or other region and change the background layer. Image credit: GFW

Once you select a country, you can add or remove the data layers you want to view for that country alone; this expedites the computer redraw and crops the data at the country’s boundaries.

2) How to view statistics on forest cover

What if you want to go beyond viewing and generate numbers or statistics on tree cover in your region of focus?

To view statistics on a particular country, navigate to the GFW home page and select “Country Profiles & Rankings.”

Country statistics on forest cover for Argentina. Image credit: GFW
Country statistics on forest cover for Argentina (forest occurs in the north and on the Pacific and southern coasts). Tabs at the bottom bring up more information. Image credit: GFW

Click on the large buttons at the right of the black header section (see image above for Argentina) to download country data or be redirected to view the data on the interactive map.

Below this initial information are tabs for other data on your selected country, including:

Each statistic and graph has a little green circle with an (I) next to it that you click for a pop-up box with information about how that data is derived.

3) How to find and download data

To download the data you are viewing online, navigate to the Open Data Portal (ODP) via this link or the ODP icon found at the top or bottom of the Interactive Map.

GFW bottom tabs & menu button
The Interactive Map’s menu of buttons, where you can access the Open Data Portal. Image credit: GFW

The ODP section of GFW uses ESRI’s Open Data to enable searches for specific data sets using keywords (just below the map), data categories (e.g. forest use data), or country names. You can view a description or metadata about each data set.

GFW ODP data categories
Categories of data available in the Open Data Portal. Image credit: GFW

You can also search for data visually by zooming in on a region of interest in an interactive map. When you start a map search, the map will present boxes showing the type and spatial extent of data sets available for that region; choose from a list of data sets below the map. You can view a given data set on a map and filter what you download either by data attributes or a particular area of the map.

Those working with spatial data can download data sets, including the main tree cover loss data, in various formats, including .CSV, .SHP, KML, JPEG, PNG and TIFF, or access the API, and add them to other mapping tools such as ArcMap, Google Earth and ArcGIS Online.

How-To drop-down menu
The How-To drop-down menu. Image credit: GFW

This GFW blog post highlights improvements to the search, view and download features made last year, with links to how and where to use them. Here is the how-to video and tutorials for the Open Data Portal.

Getting help

New users can visit GFW’s “How-To” page for tutorials, videos and instructions on how to use the various tools. Training modules and Frequently Asked Questions cover in greater detail the options mentioned here and other topics. Additionally, the GFW team welcomes feedback.


Users can also share their field data and stories via GFW crowdsourcing tools, blogs and discussion groups.

You can also overlay data layers and analyze forest change online within the GFW platform, which is helpful for those without GIS access. An upcoming post will highlight several useful tools for forest and wildlife managers.

Finally, GFW’s alert system allows you to subscribe to information from an area of the world and receive email alerts if tree cover is being lost there. This feature is also substantial enough to merit its own “basics” post–coming soon.

Intact rainforest in Isla Gorgona, Colombia
Intact rainforest in Isla Gorgona, Colombia. Photo credit: Rhett A. Butler

Other online tools

Other online tools for monitoring forests and biodiversity, which may become the focus of future posts, include:

Disclaimer:  The GFW partnership is convened by the World Resources Institute, a partner of

*NOTE that tree cover in GFW can include tree plantations that resemble forest in satellite imagery, so knowledge of an area is key to accurately identifying forest change.

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