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UNITED NATIONS SECRETARIAT
Economic and Social Affairs 03 September 2004
United Nations Expert Group Meeting to Review Critical
Issues Relevant to the Planning of the 2010 Round of Population and Housing
15-17 September 2004
GPS, Digital Imagery and GIS with Census Mapping*
By United Nations Statistics Division
* This document is being reproduced without formal editing.
1. The recent technological developments, including new high-resolution sensors, global
positioning systems (GPS), geographical information systems (GIS), Internet and World
Wide Web services, are revolutionizing cartography, surveying and mapping in
fundamental ways: geographic data is easily collected and combined with a variety of other
data in order to create relevant information for spatial analysis and decision making.
Geographic information, in its digital form, is indeed exchanged more rapidly, duplicated
without alteration, and easily disseminated to end-users.
the past decade, the United Nations Statistics Division (UNSD) has
promoting the development of geographical information systems for population and
demographic statistics in developing countries through technical cooperation projects
supported by the United Nations Fund for Population Activities (UNFPA), training
workshops, and technical publications. However, the statistical community in developing
countries has been slow to adopt the use of GIS, partially due to the monetary constraint
posed by commercial software and the availability of computers, base maps, satellite
imagery, work load, etc.
This paper outlines some developments in satellite imagery, GPS and GIS
reference to census mapping activities, and provides some insight on the similarities
between a geographic information process and a census mapping process, therefore, it urges
for the integration of these geospatial technologies within the census mapping process. It
suggests some future actions to undertake in order to help kick-start the development of this
field in developing countries.
GIS, GPS AND AERIAL AND SATELLITE IMAGERY RECENT
census symposium, held in New York in 2001, provided a comprehensive
of the significant capabilities of GPS, Satellite imagery, GIS and handheld computers, and
their relevance to census mapping operations (Dekker, 2001 and Tripathi, 2001s). Hence,
our presentation will focus on the recent developments regarding these geospatial
technologies, and specifically with regard to their better integration.
GPS, remote sensing (including aerial photography) and GIS are technologies that
being increasingly used in the field of data collection, including census mapping operations.
Until recently, aerial photography did play a major role in geographic data acquisition in
urban areas, and the use of satellite imagery, due to its low resolution, was limited to the
study of some phenomena like floods and urban pollution. However, recent satellite
imagery is extending its use to urban areas with the increase of its resolution to one-meter
(i.e. IKONOS satellite), its high positional accuracy, the revisit frequency of only three
days, and its GIS-readiness, despite their relative expensive cost (Montoya, 2002).
receivers have become popular and widespread, offering a greater accuracy at
reduced cost (a variety of units less than $500). Indeed, some cost-effective GPS can handle
real-time differential correction capable of sharpening accuracy to five meters or better.
Furthermore, GPS coordinates (waypoints) can be displayed real-time in a GIS software3
(i.e. ArcPad). GIS are becoming more powerful and friendly to use, and GPS more accurate
and cost-effective. Both are more integrated, streamlining the acquisition and processing of
coordinate data. The future of satellite positioning system looks promising, particularly
with the new system under construction, Galileo, the European system dedicated to civil
Beside GIS desktop and Internet GIS, Mobile GIS is becoming a reality. GIS
has been tailored to the needs of the field operations, allowing GIS to move from the office
to the field. Indeed, improvements in handheld computers and other portable devices, as
well as greater accuracy and the reduced cost of GPS units, have made significant
contributions to the development of mobile GIS (ArcUser, January-March 2004). With
mobile GIS, it is now possible to capture, manipulate, analyze and visualize data in the field
in real time, and ground truthing has become possible1 (see a summary on an interesting
example, illustrating how advanced mobile mapping techniques were used to delineate
census enumeration areas in Dili metropolis, Timor-Leste).
8. Furthermore, the combination of digital video (DV), satellite imagery and GPS for the
data capture and the input of this data into a GIS for manipulation, analysis and display, is
empowering data collection and integration (for ground observations of buildings, GPS can
be used in combination with digital video). Indeed, the most significant development in
these recent years lies in the better integration of GPS, image processing and GIS systems.
Hence, collecting data in the field, and storing it in a geographic database, can obviously
improve the efficiency of the census mapping process.
II. GEOGRAPHIC INFORMATION PROCESS
geographic information process consists of three stages: data acquisition,
processing and data dissemination. As illustrated in fig. 1, geospatial technologies are
spanning through these three stages: GPS and satellite imagery, among others, are useful
tools for geographic data collection; GIS have demonstrated their powerful capacities to
enable data integration, analysis, display and dissemination. Hence, remote sensing
techniques, GPS and GIS have become ubiquitous in developing policies for integrated
management (Laaribi, 2000).
Geographic information is about the management of data that are
referenced, in order to provide sound information for better decisions. Geographic
information is emerging as a fundamental part of the national infrastructure as important as
1 As the newest nation of the 21st Century, (East-Timor) faces the challenges of conducting her first
population census after independence. This paper reviews the current mapping situation in East-Timor and
presents how advanced mobile mapping techniques were used to delineate census enumeration areas in Dili
metropolis. The peculiar nature of Dili, where the issue of building ownership and property boundaries
remained contentious, coupled with the non-availability of up-to-date cadastral maps; led to a combination of
remote sensing and geographic information system techniques being used to map census enumeration areas.
QUICKBIRD high-resolution satellite imagery, GPS and an Internet enabled palm-top computer running on
windows mobile operating system together with ArcPad 6.0.2 software were used to delineate census
enumeration area maps. The methodological steps undertaken for the mobile mapping technique are narrated
in this paper and the outcomes of the pilot study are compared with the traditional census enumeration area
delineation methods. (Taiwo, 2004)