Scott Davis on Seattle NFJS Java Conference
ACT1 - Free Data Available
- Raster Data, Google Satellite
- Vector Data, Google Map
- Hybrid, Google Satellite + Google Map Hybrid mode
Type of Vectors
- Point
- Line
- Polygon
Free Vectors: www.census.gov
Shapefile: well documented proprietary ESRI standard, .shp, .shx, .dbf
Downloadable States of America: http://www.census.gov/geo/cob/bdy/st/st00shp/st99_d00_shp.zip
ESRI free viewer: http://www.esri.com/software/arcexplorer/download.html
More data, please: http://www.nationalatlas.gov
Canada: http://www.geobase.ca
For local data, most state and municipal government agencies offer free data as well.
ACT2 - Projections
Earth is round but maps are flat, projections take fundamentally 3d data and portraying it in 2-dimensions, this procedure introduce error for distance, direction, shape, area. On a Cartesian Planes, X and Y lines form perfect squares, however, on a globe, only the line of Latitude are perfectly parallel, line of Longitude converge at the poles. Different projections attempt to minimize map distortions, common projections are "State Plane" and "UTM".
Reprojection Utility available: GDAL
EPSG Codes: http://www.epsg.org
ACT3 - Spartial Databases
Why bothers with a database?
- Centralize many scattered files
- Provide security
- Indexing
- Cross dataset queries
PostgreSQL + PostGIS: http://postgis.refractions.net
Visualizing the Data: uDig
ACT4 - Web Services
- Google Maps, undeniably cool, proprietary interface
- Open set of standards available: Open Geospatial Consortium (OGC)
- OGC Features: GetCapabilities, DescribeFeatureType, GetFeature
- Data Service: WFS (Web Feature Service), WMS (Web Mapping Service)
- Open standard, any one can implement them: http://opengeospatial.org/resource/products
- GeoServer: Java based, runs in a Servlet container, provides OGC web services
- MapBuilder: Pure Javascript web client for OGC, included with GeoServer
- OpenLayers: Pure javascript web client, supports OGC, Google Maps, Yahoo Maps, MS Virtual Earth and WorldWind
