REMOTE SENSING/GIS 423 Figure Data capture and conversion from a simple field sketch map (left) to the visualization of a digital geological map (right) within GIS for the manipulation of surfaces, images, and maps in pseudo three-dimensional space, and the mathematical derivation of other products, such as slope angle, aspect or azimuth, curvature, line-of-sight, watersheds, and catchments Examples of software providing excellent 3D manipulation and viewing capabilities are ERDAS Imagine’s Virtual GIS, ER Mapper, ArcGIS 3D Analyst, and Geomatica Fly Visualization in pseudo-3D requires a valuable commodity – a digital representation of a surface, whether it is topography or other feature data, such as an interpreted seismic horizon or geophysical survey data The attribute information in this ‘surface’ layer provides the third dimension or ‘z’ value for the display There are many ways to obtain and derive digital surface topographic data or DEMs Many datasets can now be browsed and obtained on the Internet from organizations such as the United States Geological Survey and the National Imagery and Mapping Agency (NIMA) In February 2000, the Shuttle Radar Topographic Mapping Mission (SRTM) carried out radar interferometric mapping of the Earth between ỵ60 and 60 degrees latitude, in fewer than 11 days SRTM is an international project, headed by NIMA and the National Aeronautics and Space Administration (NASA), with the objective of generating global DEMs DEM data, gridded at 90 m are now available for much of the world, and at 30 m for the USA only, and are downloadable, free of charge, from ftp:// edcsgs9.cr.usgs/pub/data/srtm Sophisticated software exists (such as PCI Geomatica, Socket Set, ENVI ASTER module, Virtuozo) to generate DEMs from stereo airborne and space-borne photography and imagery One such source is Terra-1 ASTER, whose stereo capability means that high-quality DEMs can be readily generated at very low costs and at spatial resolutions suitable for 1:50 000 scale mapping (http://asterweb jpl.nasa.gov/) Geological Application Fields The application areas to which GIS makes a significant contribution are as varied as they are numerous In geosciences there are some key areas where the necessity for and contribution of GIS are clear and significant They range from the basic requirement of producing maps through the solving of complex geological challenges, to advanced spatial analysis Field Mapping The most basic of activities for the geoscientist, mapping, has been changed fundamentally through the use of GIS Though the hammer may remain ubiquitous, weatherworn field slips and notes are being replaced Field mapping essentials now include laptop and palmtop computers (Figure 3), connected to GPS hand sets (and mobile telephones) so that positional data can be fed directly and dynamically into the GIS, to record current positions for waypoints or sample localities Alternatively, tracks can be recorded as you walk along, so that you can re-trace your steps at any time, and boundaries and contacts can be walked out to provide direct mapping to the GIS database Even sketches and notes can be immediately input through palmtop graphical interfaces and handwriting transcribers These processes are commonly facilitated by Earth observation image data (from both satellite and airborne platforms), which are easily integrated in the