GRID3 Chad Settlement Extents, Version 01

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Source Center for International Earth Science Information Network; Novel-T
Contributor
Date of Dataset July 26, 2021-October 18, 2021
Updated 30 August 2021
Expected Update Frequency As needed
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Methodology

Settlement extents and associated population estimates are derived from two primary input datasets: (1) building footprints (Maxar Technologies, Inc. and Ecopia Tech Corporation. 2020. Ecopia Landbase Africa powered by Maxar. Available at DigitizeAfrica.ai), and (2) population estimates (Bondarenko M., Kerr D., Sorichetta A., and Tatem, A.J. 2020. Census/projection-disaggregated gridded population datasets for 51 countries across sub Saharan Africa in 2020 using building footprints. WorldPop, University of Southampton, UK. doi:10.5258/SOTON/WP00682 doi:10.5258/SOTON/WP00683 (UN-adjusted))

Both the settlements’ extents and classification are derived solely from Ecopia’s building footprints. Data analysis and processing were achieved entirely using Esri’s ArcGIS software (Pro version 2.7.3), it’s native module arcpy, and open source python library pandas 1.3.0.

The GRID3 Chad settlement extents are then classified (based on building density) into three classes: built-up areas (BUA), small settlement areas (SSA), and Hamlets (Barau et al., 2014). These three classes of settlement agglomerations are presented below:

Built-up areas (BUAs): A built-up area (BUA) is generally an area of urbanisation with moderately-to-densely-spaced buildings and a visible grid of streets and blocks. BUAs are characterized as polygons that maintain a 100 m2 building density of 13 or more across an area greater than or equal to 0.4 km2.

Small Settlements (SSAs): A small settlement (SSA) is a settled area of permanently inhabited structures and compounds of roughly a few hundred to a few thousand inhabitants. The housing pattern in SSAs is an assemblage of family compounds adjoining other similar habitations. SSAs areas are characterised as polygons containing 50 or more buildings and not a BUA.

Hamlet (HAMLET): A hamlet is a collection of several compounds or sleeping houses in isolation from small settlements or urban areas. Hamlets are characterised as polygons containing between 1 and 49 buildings.

See "Chad GRID3 Settlement Extents Version 01.pdf" for more details

Caveats / Comments

The “GRID3 Chad Settlement Extents, Version 01” has not been visually inspected for false negatives. A settlement may exist for a location where there is no building footprint data and consequently no settlement extent. This may lead to settlements not being identified. Likewise, the GRID3 settlement extents have not been visually inspected for false positives. A settlement polygon may have been falsely identified as an actual settlement. The type or use of buildings (e.g. residential, non-residential, mixed use, shed, etc) are not known.

GRID3 appreciates feedback regarding this dataset, such as suggestions, discovery of errors, difficulties in using the data, and format preferences.

For dataset-related questions, please send an email to GRID3: data.queries@grid3.

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