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

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

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

Disagreement in Crop/Forest Domains

Spatial disagreement

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

Estimates from different products

0

500

1000

1500

2000

2500

3000

3500

4000

Urb

an a

rea

[100

0 km

2]

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

Urban disagreement between GLC-2000 and MODIS

geo-wiki.org• Crowd-sourcing application to improve land

cover

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

urban.geo-wiki.org

Disagreement layers

Validation of urban land cover

Validation of urban land cover

GRUMP population layer

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

Validation Competition

• We will be running a competition this summer• Email me (see@iiasa.ac.at) 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

Thank you!

• For further information, please contact us:

Steffen Fritz (fritz@iiasa.ac.at)Linda See (see@iiasa.ac.at)