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Building a Crowd-sourcing Tool for the Validation of Urban Extent and Gridded
Population
Steffen Fritz, Linda See, Ian McCallum, Christian Schill, Christoph Perger and Michael Obersteiner
International Institute of Applied Systems Analysis (IIASA)Austria
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Importance of global land cover
• Global land cover is baseline information for a wide variety of application:– To delineate ecosystems – Inputs to global models of land use and land use
change, e.g. Globiom– Climate change mitigation policies e.g. REDD– Biofuel debate: where is the additional land? – Food security
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Problems with global land cover
• When different products are compared, there are lots of disagreement between them– One might say cropland, another forest
• Confusing if you are a user – which one is correct? Which is the best product to use?
• Study by Quaife et al – on veg modelling• Disagreement overall and/or spatially
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Disagreement in Crop/Forest Domains
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Spatial disagreement
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Urban areas
• Rapid urbanisation – led to many problems• > 50% of the world’s pop live in cities• By 2050, set to increase to 80% • Accurate figures needed to estimate resource
use, e.g. future carbon emissions, domestic water consumption, infrastructure, housing, etc.
• Difficult to classify
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Estimates from different products
0
500
1000
1500
2000
2500
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3500
4000
Urb
an a
rea
[100
0 km
2]
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Disagreement in the urban domain
Pairs of Land Cover Datasets Matching between Land Cover Datasets % of Total
GLC-2000 compared to MODIS
Agreement between GLC-2000 and MODIS 21.7Present in GLC-2000 and not in MODIS 17.1Present in MODIS and absent in GLC-2000 61.3
GLC-2000 compared to GlobCover
Agreement between GLC-2000 and GlobCover
29.6
Present in GLC-2000 and not in GlobCover 31.5Present in GlobCover and absent in GLC-2000
38.8
MODIS compared to GlobCover
Agreement between MODIS and GlobCover 21.4Present in MODIS and not in GlobCover 58.3Present in GlobCover and absent in MODIS 20.3
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Urban disagreement between GLC-2000 and MODIS
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geo-wiki.org• Crowd-sourcing application to improve land
cover
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Architecture
Google Earth Imagery
Land Cover Maps PostGIS Database
Client (Javascript, Google Earth API, WMS Client)
OGC Web Map Service (WMS)
Web Portal (PHP, Apache Web Server with
Gentoo Linux)
Authentication
Registered WMSserving land cover and disagreement
layers to the community
PGSQL
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urban.geo-wiki.org
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Disagreement layers
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Validation of urban land cover
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Validation of urban land cover
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GRUMP population layer
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Future Developments for urban.geo-wiki.org
• Building a hybrid map of urban areas – already carried out for the cropland domain
• Addition of other datasets– E.g. Night time luminosity, Open Street Map
• Ability to validate the population data• Addition of a gaming element• Change studies through integration of Landsat
imagery• 30 m land cover map being developed
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Validation Competition
• We will be running a competition this summer• Email me ([email protected]) or see me
afterwards and I will put you on the mailing list
• Register for urban.geo-wiki.org• Validate at least 100 points to qualify• Highest number of validations will be awarded
a prize
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Thank you!
• For further information, please contact us:
Steffen Fritz ([email protected])Linda See ([email protected])