User guide: Geospatial tools for building footprint and homogeneous zone extraction from imagery

The Global Earthquake Model (GEM) aims to provide a set of tools and models for hazard and risk analysis. The fundamental aim of the GEM Inventory Data Capture Tools (IDCT) risk global component is to provide a set of software and accompanying user protocols to enable users to collect and modify building exposure information, which can be input into the Global Exposure Database and the Global Earthquake Consequences Database.

This report describes the tools required to extract building information from remotely-sensed satellite and aerial imagery.  It provides a step-by-step user guide for a set of open-source software tools for generating data for the Global Exposure Database. IDCT has proposed an expansive suite of tools for inventory and damage collection. The opens source image processing and GIS software, Quantum GIS (QGIS) and GRASS provide the core functionality for pre-processing imagery.

Algorithms for automatically extracting building footprints are provided as a plug-in toolbar to QGIS. These have evolved from the Building RECognition tool (BREC), developed by the University of Pavia, and have been customised for use in the IDCT suite. Protocols for modifying GIS information are also provided. For regional exposure development, and generating information for use in mapping schemes, areas of homogenous land use can be manually extracted. This can also be achieved in QGIS, however the use of Google Earth for generating these data are also described.

A set of sample data are provided to allow users to test the protocols and develop their skills in generating exposure data. More details on this data can be found in Appendix C.

Remote sensing provides one of several components for developing exposure information.  Additional reports and protocols are available on the GEM website ( and NEXUS ( to partner this document, and describe the collection of building inventory and damage information from 1) in-situ field surveys, and 2) mapping schemes.