Pilote Project (OSTC - T4/12/24 )

Use of remotely satellite data for the decennial updating of the statistical sector division of Belgium

Geographic study area: The whole Belgium.

Satellite imagery used (type and co-ordinates of images purchased by OSTC):

• A selection of 59 SPOT images from the two multispectral covers of 1995 and from the panchromatic cover of 1996.

Other data:

• Vector polygons of statistical sectors and associated database with evolution of population (1981 to 1997);
• A selection of NGI orthophotoplan (Black and white – 1 m geometric resolution);
• NGI Topographic maps;
• Vector polygons of the recent communal boundaries.

Context and objectives

The Belgian National Institute of Statistics (NIS) has decided to adjust its basic census districts or statistical sectors for the 2001 census of population and housing. Indeed, many statistical sectors and agglomerations boundaries do not fit anymore because of urban growth and rural settlement development. The last updating took place with the 1981 census. It was a long and lasting job performed by traditional way based on aerial photo interpretation. The NIS wants to take advantage of new technologies to accelerate the process and make it more objective. NIS has decided to use a methodology developed by Laboratoire Surfaces and using an image processing system with SPOT satellite images and GIS software.

Methodology

The different procedures used by the method are:

• Geometrical correction of the SPOT images and division of Belgium in working areas.

• Merging of multispectral and panchromatic images;

• Tracing of the built area map by classification;

Procedure of classification in 3 stages

• Delimitation of built areas and construction of a Boolean mask; dilatation followed by erosion procedure (morphological closing) in order to regroup built areas closer than 100 meters from each other;

• Detection in rural sectors of all built nucleus from 3.0 to 9.9 ha, from 10.0 to 19.9 ha and 20.0 ha and more;

Example of all built nucleus in rural sectors from 3.0 to 9.9 ha, from 10.0 to 19.9 ha and 20.0 ha and more

• Selection of relevant high resolution digital orthophotoplans;
• Creation of new statistical sectors by heads-up digitising on top of the selected orthophotoplans;
• Trial to delimit the boundaries of urban agglomerations over 9 ha, according to 200 meter EUROSTAT distance criteria;

Outputs and Results

The main products and results delivered by the laboratory SURFACES are:

• a digital cartography with built areas appeared in dispersed settlements sectors;
• a selection of relevant orthophotoplans;
• a digital cartography with a trial of urban agglomeration boundaries determined according to 200 meters EUROSTAT criteria;

• a trained staff.

These deliverables help the NIS to finalise the statistical area partition, to determine its content in terms of street sections and buildings for the 2001 census.

Table 1. :        Nucleuses of build area in dispersed settlements sectors

Execution:

Period: Two years (1998-99)

Laboratory:                Laboratoire SURFACES

Département de Géomatique

Université de Liège

URL laboratory:        http://www.geo.ulg.ac.be/

Userpartners:             The Belgian National Institute of Statistics (NIS)

Ministry of economic affairs.

URL:                           http://statbel.fgov.be/

Discipline :

Land planning & infrastructures

Urban & suburban

Cartography

Economic issues

Agriculture

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