risk:exposure:dwelling_fractions [SARA Wiki]

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====== Dwelling fractions ======

For the present model, the source of information for number of dwellings was the latest census survey for each country. A summary of the available data for the different administrative levels is presented in the following table, along with the number of attributes considered when downloading data.

The following attributes were used to assign a building class to the different dwellings identified in the census:\\
i) predominant material of the exterior walls,\\
ii) material of the floor,\\
iii) type of dwelling, and\\
iv) type of area (urban or rural).

None of the surveys included information about the number of storeys, nor the lateral load resisting system, and only the housing census data from Venezuela made reference to the year of construction. The reason for using four attributes was due to the possibility to download disaggregated data from the databases of each country. For Colombia and Venezuela, the type of dwelling was not included because disaggregation of data was only available for a maximum of three attributes.
Note that the first version of the regional mapping scheme for South America presented in the previous progress report only considered two attributes for building classification: the predominant material of the exterior walls and the material of the floors.

{{:census_information.png?nolink&500}}

After analysing the available information in the census surveys, it became clear that certain categories could be associated to more than one of the [[risk:exposure#definition_of_building_classes|building classes]]. For example, dwellings whose predominant exterior wall material was defined as clay bricks could be assigned to reinforced concrete moment-frame, to confined or unreinforced wall masonry structure. Moreover, these classes could be further divided based on the number of storeys and level of ductility. Thus, it was necessary to establish a relationship between the attributes used in the census data, and the list of building classes. This relationship can be named as a [[risk:exposure:mapping|mapping scheme]].


In brief, for each country two mapping schemes were produced: one for urban areas and one for rural areas. Each mapping scheme consists of two tables: the first table assigns an initial building group according to the material of the exterior walls and the material of the floor; then the second table assigns the dwelling fractions according to the initial building group and the type of dwelling (Colombia and Venezuela do not have the second table). Finally, by multiplying the number of dwellings times the dwelling fractions, the number of dwellings per building typology is calculated at each geographical scale. The building typologies have been defined in accordance with the [[http://www.globalquakemodel.org/resources/publications/technical-reports/gem-building-taxonomy-report/|GEM Building Taxonomy v2.0]].

A new mapping scheme has been established for each country taking into account the information available in the Global Exposure Database (GED, that includes PAGER and UN-HABITAT building fractions), the housing reports from the World Housing Encyclopedia (WHE), the results coming from the exposure session of the GEM workshop at Medellin and national and sub-national datasets (census information).

__**[[risk:exposure:mapping|...see more about mapping scheme methodology]]**__

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