This document summarizes a study analyzing the adequacy of geotagged Flickr photos for helping quality control of land cover maps. The study analyzed the temporal, spatial, and land cover class distributions of over 400,000 Flickr photos in Portugal between 2004-2012. Key findings include an uneven spatial distribution of photos across municipalities, higher densities in artificial and water classes, and potential but also limitations for validating land cover maps when used alone due to irregularities. Combining multiple volunteer data sources may help address limitations.

1. Nome e/ou Título e/ou Outros25-06-2013 1
Flickr geotagged and publicly available photos:
preliminary study of its adequacy for helping
quality control of Corine Land Cover
Jacinto Estima and Marco Painho
Jacinto.estima@gmail.com; painho@isegi.unl.pt
www.isegi.unl.pt
Eighth International Conference on "Geographical Analysis, Urban Modeling, Spatial Statistics“ GEOG-AND-MOD 13
2013 International Conference on Computational Science and its Applications (ICCSA 2013)
June 24th
- June 27th
, 2013 - International University, Ho Chi Minh City, Vietnam

2. Agenda
• Introduction
• Objective
• Related work:
– Volunteered Geographic Information
– Land Use/Cover mapping
– VGI and Land Cover mapping
• Material and Methods
• Results and Discussion
• Conclusions and Future Work
25-06-2013 2
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

3. Introduction
• Land Use/Cover (LULC) mapping plays a very important role in a
vast number of research fields
• Produced based on interpretation and classification of remote
sensing data, made by highly skilled people
• “Ground truth” information is required in some phases
• Since 2005 the spatial data produced by volunteers became
exponentially available over the Web - great opportunity
• Some challenges related with its heterogeneity, quality control and
metadata absence, etc.
25-06-2013 3
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

4. Objective
• Preliminary analysis of the adequacy of photos from the
Flickr initiative in order to use them as a source of field
data in the quality control of the LULC databases:
– Analyze this source in terms of its temporal and spatial
distribution and also its distribution over the different LULC
classes
25-06-2013 4
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

5. Background (1)
• Volunteered Geographic Information
– Geographic Information (GI) has been produced by mapping
agencies and corporations
– This approach is very expensive favoring the most important and
unchanging geographic themes
– Google Maps was a revolution
– Cheaper positioning devices combined with camera and mobile
or smart phones, fine resolution-imagery, broad band
communications, are empowering citizens to produce and share
their own maps
25-06-2013 5
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

6. Background (2)
• Volunteered Geographic Information
– Several terminologies arise always related with a type of User
Generated Content (UGC) that deals with spatial content
• Neogeography (Tuner, 2006)
• Volunteered Geographic Information (Goodchild, 2007)
• Crowdsourcing Geospatial (Hudson-Smith, Batty, Crooks, & Milton,
2009)
– The specialist meeting held in Santa Barbara, CA in December
2007, organized by the National Center for Geographic
Information and Analysis (NCGIA) proved the importance of
this type of data
25-06-2013 6
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

7. Background (3)
• Volunteered Geographic Information
– The participation and contribution of citizens in this filed is not
new:
• 1930s when teachers and school children contributed to land use
surveys of Britain
• urban residents involved in the Bunge's “Geographical Expeditions”
in 1971
• ‘‘Did you feel it?’’ - portal established by the USGS Earthquake
Hazards Program for earthquake mapping (1999)
– Elwood et al. (2011) counted ninety-nine VGI initiatives, 70% of
them started after 2005
– 2005 can be considered a turn point
25-06-2013 7
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

8. Background (4)
• Land Use/Cover mapping
– According to Cihlar (2000) LULC mapping consists of four main
steps: data acquisition, pre-processing, analysis/classification,
and product generation and documentation
– The analysis/classification phase must end with the Accuracy
Assessment (AA)
– AA is made by confronting the produced cartography with
reference information assumed as true
– Very important task to offer map quality indicators
– Field work is needed (increases the cost and the time)
25-06-2013 8
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

9. Background (5)
• VGI and Land Cover mapping
– Geo-Wiki.Org is one project described as a global network of
volunteers who wish to help improving the quality of global land
cover maps
– Virtual Interpretation of Earth Web-Interface Tool (VIEW-IT) for
Collecting Land-Use/Land-Cover (LULC) Reference Data is
another initiative still as “a proof of concept”
– More recently, in 2010, Leung and Newsam conducted some
experiments to derive maps of “what-is-where” from large
collections of georeferenced photos in an automated way
25-06-2013 9
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

10. Study area and Datasets (1)
• Study area
– The study area is Continental Portugal
– The land cover is mainly composed by agricultural and forest
areas (around 95%)
• Datasets (Fig. 1)
– Geo-referenced and publicly available Flickr photos’ locations
• Downloaded 414,323 and used 409,829 after pre-processing
• study period ranging between 2004 and 2012
– Corine Land Cover (CLC) database for the CLC2006 inventory -
version 16 (04/2012) – raster format
– Portuguese official administrative boundaries database - “Carta
Administrativa Oficial de Portugal” (CAOP) – vector format
25-06-2013 10
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

11. Study area and Datasets (2)
25-06-2013 11
a)
c)
b
)
Fig. 1. Datasets used: a) CAOP database, b) Flickr photos’ locations, c) CLC database.
a) b) c)
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

12. Study area and Datasets (3)
25-06-2013 12
a)
c)
b
)
Level 1 Area (Km2
) Level 2 Area (Km2
)
1 Artificial surfaces 3088.01
11 Urban fabric 2274.38
12 Industrial, commercial and transport units 472.44
13 Mine, dump and construction sites 210.25
14 Artificial, non-agricultural vegetated areas 130.94
2 Agricultural areas 41996.50
21 Arable land 12444.56
22 Permanent crops 5938.69
23 Pastures 418.06
24 Heterogeneous agricultural areas 23195.19
3 Forest and semi
natural areas 42620.95
31 Forests 20171.63
32 Scrub or herbaceous vegetation 20776.13
33 Open spaces with little or no vegetation 1673.19
4 Wetlands 1012.31
41 Inland wetlands 258.06
42 Maritime wetlands 754.25
5 Water bodies 361.75
51 Inland waters 351.06
52 Marine waters 10.69
Table 2. CLC nomenclature for level’s 1 and 2 (source: http://www.igeo.pt/gdr/pdf/CLC2006_nomenclature_addendum.pdf)
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

13. Methods
• Analysis of the temporal distribution of Flickr photos
• Analysis of the spatial distribution by confronting the
photos with the Portuguese municipalities
• Analysis of the distribution over the different CLC
classes
• Cross analysis to compare the distribution of photos over
CLC classes along with the spatial and temporal
distributions
25-06-2013 13
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

14. Results (1)
• Temporal distribution of the Flickr photos
25-06-2013 14
Fig. 2. Number of Flickr photos per year (a); monthly average of Flickr photos between 2004 and 2012 (b).
a)
b)
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

15. Results (2)
25-06-2013 15
Fig. 3. Flickr photos
frequency distribution by
municipalities: absolute
number of photos (a)
and normalized by area
(b).
a) b)
Spatial
distribution of
Flickr photo
locations
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

16. Results (3)
25-06-2013 16
Fig. 4. Spatial distribution of Flickr photos over
the municipalities of Lisboa (a), Pedrógão
Grande (b) and Vimioso (c).
Spatial distribution of
Flickr photo locations
a)
b)
c)
c)
b)
a)
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

17. Results (4)
• Distribution of Flickr photo locations over CLC classes
25-06-2013 17
Level 1 classes Area (Km2
) Num. photos Perc. Density (photos/Km2
)
1 Artificial surfaces 3088.01 322032 78.58% 104.28
2 Agricultural areas 41996.50 34270 8.36% 0.82
3 Forest and semi natural areas 42620.95 37129 9.06% 0.87
4 Wetlands 1012.31 2902 0.71% 2.87
5 Water bodies 361.75 13496 3.29% 37.31
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

18. Results (5)
• Distribution of Flickr photo locations over CLC classes
25-06-2013 18
CLC Level 2 classes Frequency Percentage
11 Urban fabric 248866 60.72%
12 Industrial, commercial and transport units 34283 8.37%
13 Mine, dump and construction sites 408 0.10%
14 Artificial, non-agricultural vegetated areas 38475 9.39%
21 Arable land 5373 1.31%
22 Permanent crops 5094 1.24%
23 Pastures 426 0.10%
24 Heterogeneous agricultural areas 23377 5.70%
31 Forests 16709 4.08%
32 Scrub and/or herbaceous vegetation associations 12756 3.11%
33 Open spaces with little or no vegetation 7664 1.87%
41 Inland wetlands 37 0.01%
42 Maritime wetlands 2865 0.70%
51 Inland waters 6636 1.62%
52 Marine waters 6860 1.67%
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

19. Results (6)
• Cross analysis
25-06-2013 19
Fig. 5. Monthly
distribution of
photos in each CLC
level 1 class.
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

20. Results (7)
• Cross analysis
25-06-2013 20
Fig. 6. Monthly
variation of photos
by district.
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

21. Results (8)
25-06-2013 21
District
Min Max
Ratio
Month Value Month Value
Aveiro May 439 Oct 1748 3.98
Beja Feb 140 Jul 1607 11.48
Braga Jan 832 Aug 2382 2.86
Bragança Jan 18 Jul 471 26.17
Castelo Branco Mar 119 Aug 806 6.77
Coimbra Nov 569 Aug 1542 2.71
Evora Jan 328 Sep 897 2.73
Faro Dec 1118 Jul 4669 4.18
Guarda Jun 109 Aug 808 7.41
Leiria Feb 536 Aug 2340 4.37
Lisboa Jan 11018 Sep 21630 1.96
Portalegre Feb 137 Aug 491 3.58
Porto Jan 3247 Sep 7560 2.33
Santarem Feb 197 Sep 1007 5.11
Setubal Feb 1239 Sep 2573 2.08
Viana do Castelo Feb 221 Aug 1413 6.39
Vila Real Jan 154 Aug 596 3.87
Viseu Nov 173 Aug 798 4.61
Cross
analysis
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

22. Conclusions
• Large number of georeferenced photos available
• Spatial asymmetry and irregular distribution of the data
was confirmed
• Irregular distribution over different CLC classes
• Temporal distribution is the most positive characteristic
• This resource cannot be used alone for the purpose of
helping the AA phase of LULC production
• Some potential has been demonstrated and we truly
believe that the solution could be to combine different
sources of VGI
25-06-2013 22
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

23. Future work
• Study and analysis of other VGI sources
• Extend the study area to Europe in order to characterize
a broader area and verify differences between countries.
• Characterization of the content of title and other
descriptive tags
• A data model able to integrate all the suitable VGI should
be further investigated and developed.
25-06-2013 23
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

24. Acknowledgements
This research has been partially supported by COST Action
TD1202, Mapping and the Citizen Sensor.
25-06-2013 24
GEOG-AND-MOD 13 • ICCSA 2013
June 25th - June 27th, 2013 - International University, Ho Chi Minh City, Vietnam

25. Nome e/ou Título e/ou Outros25-06-2013 25
Thank you for your attention
cảm ơn bạn đã quan tâm của bạn
Jacinto Estima and Marco Painho
Jacinto.estima@gmail.com; painho@isegi.unl.pt
www.isegi.unl.pt
Eighth International Conference on "Geographical Analysis, Urban Modeling, Spatial Statistics“ GEOG-AND-MOD 13
2013 International Conference on Computational Science and its Applications (ICCSA 2013)
June 24th
- June 27th
, 2013 - International University, Ho Chi Minh City, Vietnam