Abstract
Web-based applications that integrate geospatial information, or the geoweb, offer exciting opportunities for remote sensing science. One such application is a Web‑based system for automating the collection of reference data for producing and verifying the accuracy of land-use/land-cover (LULC) maps derived from satellite imagery. Here we describe the capabilities and technical components of the Virtual Interpretation of Earth Web-Interface Tool (VIEW-IT), a collaborative browser-based tool for “crowdsourcing” interpretation of reference data from high resolution imagery. The principal component of VIEW-IT is the Google Earth plug-in, which allows users to visually estimate percent cover of seven basic LULC classes within a sample grid. The current system provides a 250 m square sample to match the resolution of MODIS satellite data, although other scales could be easily accommodated. Using VIEW-IT, a team of 23 student and 7 expert interpreters collected over 46,000 reference samples across Latin America and the Caribbean. Samples covered all biomes, avoided spatial autocorrelation, and spanned years 2000 to 2010. By embedding Google Earth within a Web-based application with an intuitive user interface, basic interpretation criteria, distributed Internet access, server-side storage, and automated error-checking, VIEW-IT provides a time and cost efficient means of collecting a large dataset of samples across space and time. When matched with predictor variables from satellite imagery, these data can provide robust mapping algorithm calibration and accuracy assessment. This development is particularly important for regional to global scale LULC mapping efforts, which have traditionally relied on sparse sampling of medium resolution imagery and products for reference data. Our ultimate goal is to make VIEW-IT available to all users to promote rigorous, global land-change monitoring.
Highlights
Web-based applications that use geospatial information—part of the ―geoweb‖—are evolving at a rapid pace, especially with the rise of open-source web mapping services and associated application programming interfaces (APIs), such as the Google Maps API released in 2005
Other JavaScript APIs integrated into Virtual Interpretation of Earth Web-Interface Tool (VIEW-IT) include (Figure 1): Panoramio to view georeferenced (e.g., ―geo-tagged‖) photographs uploaded by a global community; Google Charts for viewing temporal Enhanced Vegetation Index (EVI) data at sample points and administration data summary; and, ArcGIS JavaScript API for displaying biome and ecoregion polygon and VIEW-IT sample points GIS layers from ArcGIS Server 9.3 (ESRI, Inc.)
The cross-checking of independent user interpretations and expert review tools helps to improve the accuracy of reference samples, especially when combined with an iterative training of users by expert users
Summary
Web-based applications that use geospatial information—part of the ―geoweb‖—are evolving at a rapid pace, especially with the rise of open-source web mapping services and associated application programming interfaces (APIs), such as the Google Maps API released in 2005(code.google.com/apis/maps). The technology can allow multiple users to collaborate in collecting geospatial information in a Web-based platform [4,5,6]. Examples of Web-based VGI include OpenStreetMap (www.openstreetmap.org), Google Map Maker (mapmaker.google.com), E-Flora Geoweb sites allow users to browse and visualize remote sensing products across broad areas with simple user interfaces, and can offer base imagery and other map layers that provide geographic context. These map services are generally cached for quick display with relatively slow Internet connections.
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