Using geobrowsers for thematic mapping
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The document discusses using geobrowsers for thematic mapping. It examines the current capabilities of geobrowsers like Google Earth and Google Maps for thematic mapping. It also explores how thematic mapping could be better supported in geobrowsers through techniques like choropleth maps, proportional symbol maps, and using the third dimension. The author developed a Thematic Mapping Engine to generate thematic maps in geobrowsers using open data and standards.
Using geobrowsers for thematic mapping
- 1. Using geobrowsers for thematic mapping Bjørn Sandvik MSc in Geographical Information Science University of Edinburgh Postgraduate Research Conference 17-19 March 2008 Supervisors: Bruce Gittings and James Reid
- 2. Research questions What are the current capabilities for thematic mapping in geobrowsers? How could thematic mapping be better supported by geobrowsers? GIS & Web standards Thematic mapping Geo- browsers Public datasets Visualisations
- 3. What are thematic maps? Choropleth maps Proportional symbol maps Graph symbol maps Animated maps (temporal) Flow maps Dot maps Isarithmic maps Dasymetric maps Cartograms Univariate maps (1) Bivariate maps (2) Multivariate maps (3+)
- 4. What is a geobrowser? Google Earth Google Maps OpenLayers Microsoft Virtual Earth ArcGIS Explorer NASA World Wind Yahoo! Maps 3D vs. 2D
- 5. Why use geobrowsers for thematic mapping? Easy to use Embeddable Support both raster and vectors Can combine dataset from various sources Sperical projection (3D) ” Earth feeling” Free Why not? To much information? Technical restrictions? Lack of OGC standards support? Ad intrusion?
- 6. Thematic Mapping Engine Thematic Mapping Parameters OpenLayers PHP Library Web Interface Web Processing Service Thematic Mapping Engine
- 7. Choropleth map in Google Earth $map = new ThematicMap(); $map->setType("choropleth"); $map->addData($values); $map->addBorders($borders); $map->setColourRange($colors); $kml = $map->getKML(); Data source: UNdata
- 8. Using the 3rd dimension $kml = $map->getKML(‘3D’); Data source: UNdata
- 9. Proportional symbol maps $map->setType(“symbol"); $map->setBasenam($basemap); $map->setSymbolSize(”pop”); Data source: UNdata and Tom Patterson
- 10. Challenge 1: polygon holes Data source: UNdata
- 11. Challenge 2: Mercator Can OpenLayers do better?
- 13. Challenge 4: Complexity function kmlSymbolCalculator( $longitude, $latitude, $distance, $points, $altitude ) { $EARTH_RADIUS_EQUATOR = 6378140.0; $RADIAN = 180 / pi(); $long = $longitude; $lat = $latitude; $long = $long / $RADIAN; $lat = $lat / $RADIAN; $f = 1/298.257; $e = 0.08181922; $kml = '<Polygon>' . PHP_EOL . ' <outerBoundaryIs>' . PHP_EOL . ' <LinearRing>' . PHP_EOL . ' <coordinates>'; for ( $bearing = 0; $bearing <= 360; $bearing += 360/$points) { $b = $bearing / $RADIAN; $R = $EARTH_RADIUS_EQUATOR * (1 - $e * $e) / pow( (1 - $e*$e * pow(sin($lat),2)), 1.5); $psi = $distance/$R; $phi = pi()/2 - $lat; $arccos = cos($psi) * cos($phi) + sin($psi) * sin($phi) * cos($b); $latA = (pi()/2 - acos($arccos)) * $RADIAN; $arcsin = sin($b) * sin($psi) / sin($phi); $longA = ($long - asin($arcsin)) * $RADIAN; $kml .= " ".$longA.",".$latA; } $kml .= ' </coordinates>' . PHP_EOL . ' </LinearRing>' . PHP_EOL . ' </outerBoundaryIs>' . PHP_EOL; return $kml; }
- 15. Best to follow standards? Thematic Mapping Engine DDI/DCMI SDMX Metadata ISO 19115:2003 OGC SLD/SE extension? Best practices Thematic mapping techniques GML / WFS WKT / WKB GeoJSON XML CSV Array JSON TMS Parameters Storage Data in Data out Geobrowser WMS Map Tiles KML WFS / GML GeoJSON GeoRSS
- 16. Open philosophies Open Source Open Data Open Access My sins Access for all Redistribution Vectors… Saved by UNdata… “ All data and metadata provided on UNdata’s website are available free of charge and may be copied freely , duplicated and further distributed provided that they are not put up for sale or otherwise commercially exploited and that UNdata is cited as the reference.”
- 17. GIS democratisation “ Central control of computer databases, such as GIS, tend to increase the power to the bureaucrats, administrators, technical experts and computer literate groups who use them at the expense of those who lack the expertise to access to these systems” (Arnoff, 1989, p. 285) “ Those with best access to knowledge and efficient information processing gain economic, military and political advantage over those lagging it.” (Onsrud, 1985)
- 18. Exploratory mapping ” Mapping should proceed through multiple, competing visualisations which are not created by the cartographer and transmitted to the user, but made on the spot by the user acting as his or her own cartographer” - Jeremy Cramption My dissertation: Give the data, the cartographic toolbox and the visualisation tools to the user in a web-based interface.
- 19. Website and blog thematicmapping.org