anchor.diff:                <p>Viewing data for the first period available via the time slider may include alerts that reflect detections from the February 2000 to December 2005 training period as the algorithm "catches up" post-training. </p>
                 <p>The GFW team has clipped out some data in regions where data quality is suspected to be low because of persistent cloud cover over identified ecoregions. This covers parts of Liberia, Venezuela, Guyana, Vietnam, Laos, and Burma/Myanmar. The current extent of the FORMA alerts is available for viewing here—<a href='http://wri-01.cartodb.com/viz/3cc0f4c2-56d3-11e3-80bb-c8600054c0d1/embed_map?title=true&description=true&search=false&shareable=false&cartodb_logo=false&layer_selector=false&legends=false&scrollwheel=true&sublayer_options=1&sql=&zoom=3&center_lat=-1.845383988573187&center_lon=16.34765625' target='_blank'>FORMA geographic extent</a>.</p>
                 <p>The <a href='https://github.com/wri/forma-clj' target='_blank'>algorithm</a> behind the FORMA alerts is constantly evolving to fix bugs and improve accuracy. As a result, what appears on the site and the results of analyses conducted on the site may change over time. It is important to always include the access date when citing FORMA. For questions, please contact <a href='mailto:gfw@wri.org'>gfw@wri.org</a>.</p>
  +              <p>For the purpose of this study, “tree cover” was defined as areas with greater than 25% canopy cover (as defined by the <a href='http://journals.ametsoc.org/doi/abs/10.1175/1087-3562(2003)007%3C0001%3AGPTCAA%3E2.0.CO%3B2' target='_blank'>Vegetation Continuous Fields data set</a>), and change was measured without regard to forest land use. Tree cover assemblages that meet the 25% threshold include intact forests, plantations, and forest regrowth.</p>
                 <p>When zoomed out, this data layer displays some degree of inaccuracy because the data points must be collapsed to be visible on a larger scale. Zoom in for greater detail.</p>
               </dd>
             </dl>
  
positive.code:         <div class='source_table'>
            <dl class='sources_row'>
              <dt>Function</dt>
              <dd>Detects areas where forest clearing is likely to have recently occurred</dd>
            </dl>
            <dl class='sources_row even'>
              <dt>Resolution/scale</dt>
  
negative.code: 
          <div class='source_extended'>
            <h3 class='overview_title'>Methodology</h3>
            <p>This dataset uses freely available satellite imagery, collected by the <a href='http://modis.gsfc.nasa.gov/about/' target='_blank'>Moderate Resolution Imaging Spectroradiometer (MODIS)</a>, which operates on NASA's Terra and Aqua (EOS PM) satellite platforms and views the entire Earth’s surface every 1 to 2 days. The images help to reveal notable changes in vegetation cover over time using an indicator that measures vegetation intensity called the <a href='http://earthobservatory.nasa.gov/Features/MeasuringVegetation/measuring_vegetation_2.php' target='_blank'>Normalized Difference Vegetation Index (NDVI)</a>. By applying an automated algorithm to this input and in combination with complementary data inputs for fire hotspots and global precipitation averages, areas where tree cover loss is likely to have occurred are therefore identified. The algorithm also employs parallel processing in a remote server system the cloud that enables the rapid analysis of these very large data sets.</p>
  
            <h3 class='overview_title'>Explanation</h3>
            <p>Tree cover loss alerts appear when and where new, large-scale loss is likely to have occurred after 2005. Thus the alerts should not be interpreted as an analysis of total tree cover loss area but rather as an indication of an area that has a high probability of having experienced tree cover loss or disturbance over time. The system employs advanced statistical techniques to achieve the best fit to scientifically validate information on loss, measured as a probability. On the GFW website, alerts appear only for 50% or higher probability. That is, alerts appear for a particular period when there has been significant loss in the area during or before that period.</p>
  
            <h3 class='overview_title'>Temporal and spatial resolution</h3>
            <p>FORMA alerts are displayed on the GFW site as monthly data, and the site is updated each month. Users who download data for analysis will find that the underlying data set is actually available at 16-day intervals, intervals that do not line up perfectly with calendar months. Data is displayed at a monthly resolution on GFW due to the monthly availability of precipitation data input. Users can manipulate the GFW time slider to view trends in loss alerts from December 2005 to present.</p>
  
            <p>The alert system currently identifies 500 x 500 meter areas where loss is statistically likely to have occurred. Alerts for a 250-meter resolution version are currently being developed on Google’s Earth Engine platform and will be available in 2014.</p>
  
            <h3 class='overview_title'>Geographic extent</h3>
            <p>FORMA alerts are currently available only for humid tropical forests (as defined by <a href='http://www.pnas.org/content/105/27/9439.full#ref-1' target='_blank'>Hansen et al. (2008)</a>, based on <a href='http://wolfweb.unr.edu/~ldyer/classes/396/olsonetal.pdf' target='_blank'>WWF’s terrestrial ecoregions</a>) spanning portions of 89 countries. The development team is working to incorporate additional data to extend the geographic coverage beyond the current extent. To visualize the geographic extent of the alerts on the map, switch on the “Humid Tropical Forest Biome” layer.</p>
  
            <h3 class='overview_title'>Data applications</h3>
            <p>The alerts have been designed for quick identification of tree cover loss as it happens. This allows for rapid response and prioritization of scarce financial and human resources dedicated to forest conservation or sustainable forest management. Armed with this information, stakeholders can use preemptive methods such as on-the-ground visits or aerial inspection with high-resolution satellite imagery (less than 5-meter pixel resolution) to investigate suspected tree cover loss areas.</p>
  
            <p>In addition, the alerts may be of value to a variety of researchers who study both temporal and spatial patterns related to tree cover loss areas.</p>
  
            <p>Using the GFW platform, the alerts can be compared against other relevant data layers, such as protected areas and concessions boundaries, to evaluate the effectiveness of forest management practices across time and spatial extent.</p>
  
            <h3 class='overview_title'>Accuracy and validation</h3>
            <p>Inaccuracies are an inherent part of remote sensing analysis. FORMA alerts appear in areas with a greater than 50% probability of deforestation, based on the algorithm described under Methodology. However, persistent cloud cover is a continuous issue in the tropics, and extreme flooding can also produce unreliable remotely sensed data that will result in tree cover loss “false positives” (alerts where no actual tree cover loss has occurred). Furthermore, the alerting system cannot detect all forest cover loss, whether due to the small size of the loss area, persistent cloud cover, or other explanations still being identified through GFW validation efforts.</p>
  
            <p>The major instances of false positives may occur as the following:</p>
  
  