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This seminar covers the different techniques for collecting geospatial data in GIS, including primary and secondary methods such as geocoding, raster and vector capture. It also discusses the challenges of data collection and provides tips for finding georeferenced data online.
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Geografiske informasjonssystemer (GIS)SGO1910 & SGO4930 Vår 2004 Foreleser: Karen O’Brien (karen.obrien@cicero.uio.no) Seminarleder: Gunnar Berglund (gunnarbe@student.sv.uio.no)
Data Collection • One of most expensive GIS activities • Many diverse sources • Two broad types of collection • Data capture (direct collection) • Data transfer • Two broad capture methods • Primary (direct measurement) • Secondary (indirect derivation)
GEOCODING • Geocoding is the conversion of spatial information into digital form. • Geocoding involves capturing the map, and sometimes also capturing the attributes.
Primary Data Capture • Capture specifically for GIS use • Raster – remote sensing • e.g. SPOT and IKONOS satellites and aerial photography • Passive and active sensors • Resolution is key consideration • Spatial • Spectral • Temporal
Secondary Geographic Data Capture • Data collected for other purposes can be converted for use in GIS • Raster conversion • Scanning of maps, aerial photographs, documents, etc • Important scanning parameters are spatial and spectral (bit depth) resolution
Vector Primary Data Capture • Surveying • Locations of objects determines by angle and distance measurements from known locations • Uses expensive field equipment and crews • Most accurate method for large scale, small areas • GPS • Collection of satellites used to fix locations on Earth’s surface • Differential GPS used to improve accuracy
Vector Secondary Data Capture • Collection of vector objects from maps, photographs, plans, etc. • Digitizing • Manual (table) • Heads-up and vectorization • Photogrammetry – the science and technology of making measurements from photographs, etc. • COGO – Coordinate Geometry (land records and property lots – precise measurements: vector)
Summary • Data collection is very expensive, time-consuming, tedious and error prone • Good procedures required for large scale collection projects • Main techniques • Primary • Raster – e.g. remote sensing • Vector – e.g. field survey • Secondary • Raster – e.g. scanning • Vector – e.g. table digitizing
Searching for georeferenced data • First explore the Internet to find possible sources of data • Second, contact organizations or research institutions (kommuner, Statenskartverk, UNEP, etc.)
Example #1 • Data for Sør Fron kommune
4. DEK • Alle eiendomsgrenser fra ØK er nå ferdig digitalisert i Oppland, men det gjenstår mye når det gjelder digitalisering av kommunale data(gamle målebrev og lignende). Sluttkontroll er levert alle kommuner, og mange har en jobb å gjøre her! Det er mulig å forbedre DEK ved å kjøre diverse kontroller mot GAB, se vedlagte foiler. Ta kontakt med Kari Anne dersom noen trenger hjelp til å komme i gang, eller ønsker en hospiteringsordning. Telefon 61 26 62 13.
Example 2 • Data for Costa Rica
Challenge: • Think about a place for which you would like to get georeferenced data, and do some searching on the Internet.
