5: Data Sources for GIS Flashcards
WHAT IS DATA CAPTURE
Process of getting data from the world into the GIS
KEY STAGES IN DATA COLLECTION
Planning - decide what data is needed Preparation - get the data sources Digitising / transfer - bring into computer Editing / Improvement - clean Evaluation - verify it
LIST SOURCES FOR PRIMARY AND SECONDARY DATA CAPTURE
Primary: Field survey remote sensing GPS LiDAR Satellites
Secondary: Scanning paper maps Digitising maps Scanned photographs Crowd sourcing Census data GIS data libraries
GIVE EXAMPLES OF GIS DATA TRANSFERS
Translation
source file to intermediate file to GIS
Direct Read
source file to GIS
LIST KEY COMPONENTS OF METADATA
what is the age of the data?
where did it come from?
what is the spatial extent?
what is the projection coordinate system, and datum?
what is the spatial resolution (density of observation)?
what is the accuracy and precision?
what is the file format?
who collected the data?
has the data been checked/verified?
has it been updated since being collected?
what’s the reliability of the person who collected it?
What is metadata?
data about data
What are some techniques to prepare data from secondary sources for use in GIS?
Digitising
Scanning
Data transfer
Keycoding
Two types of data
Analogue:
Tabular data, map data, aerial photographs, field surveys
Digital:
Tabular data, map data, aerial photographs, GPS, satellite imagery
Data capture sources and data model types
Primary Vector:
GPS measurements or field survey measurements
Secondary Vector:
topographic maps
toponymy (place-name) databases
digitised maps
Primary Raster:
digital satellite imagery or aerial photographs
Secondary Raster:
scanned maps or photos
digital elevation model from topographic map contours
Primary raster data capture
Remote sensing techniques
- satellites and aerial photography
- measure electromagnetic radiation
- passive and active sensors
Resolution is depend on:
- spatial (pixels)
- spectral (EMR)
- temporal (frequency)
Primary data capture: raster examples
Remote sensing techniques
- satellites and aerial photography
- measure electromagnetic radiation
- passive and activity sensors
Resolution is depend on:
- spatial (pixels)
- spectral (EMR)
- temporal (frequency)
Primary data capture: vector examples
Surveying
- location of objects determined by angle and distance
- measurements relative to known locations
- field equipment + crews
GPS
- uses satellites to fix location on earth’s surface
- differential GPS used to improve accuracy
LiDAR
- transmits EMR
- measures radiation scattering back to receiever after interacting with earth’s surface/vegetation
- generates a point cloud
Primary data capture: raster examples (1)
Remote sensing techniques
- satellites and aerial photography
- measure electromagnetic radiation
- passive and activity sensors
Resolution is depend on:
- spatial (pixels)
- spectral (EMR)
- temporal (frequency)
Primary data capture: vector examples (3)
Surveying
- location of objects determined by angle and distance
- measurements relative to known locations
- field equipment + crews
GPS
- uses satellites to fix location on earth’s surface
- differential GPS used to improve accuracy
LiDAR
- transmits EMR
- measures radiation scattering back to receiver after interacting with earth’s surface/vegetation
- generates a point cloud
Secondary data capture (raster and vector)
Data collected for other purposes that can be converted for use in GIS
Raster Conversion:
Scanning of maps, aerials, photographs, documents, etc
Scanning parameters:
- spatial resolution (dpi)
- spectral resolution (bit depth)
- subject to distortion!!
Vector Conversion:
Digitising vectors from hard copy/scanned maps, photos and plans
Human errors in digitising
undershoots and overshoots
dangling segment
invalid polygons
sliver polygons
How to fix: data cleaning algorithms or manual cleaning
Photogrammetry
create a 3D scene from photographs
Attribute data sources (4)
Field surveys
-markeing data from interviews (health/crime/safety)
Government statistics
- statistics collected and reported by gov (Stats NZ, NZ police, immigration)
- CENSUS
Government admin records
-records collected by gov as part of admin functions like tax, auto rego, property taxes
Crowd Sourcing
- citizen science projects (bird census)
- volunteered geographic info (open street map)
