Appendix 4 167
Step-By-Step Description of Map Construction Model Space • Cells were defined as 28.5 meter by 28.5 meter squares, following work done by the Lincoln Land Institute (Angel et al., 2010). • All data sets were projected into the Albers Equal Area Conic projection and aligned to a digital elevation model raster. • All vector data were converted to raster data. • The modeling extent was defined by a 20-kilometer buffer around the urban area from the most recent time period. • All operations were executed in Python programming language or the ArcGIS 10 software suite using tools from ArcGIS 10 (Esri, 2011) and Python scripts. Definition of Urban Extent over Time • Primary input data sets: existing urban areas were defined through digitization of satellite imagery for 31 cities for three time periods (as close to 1990, 2000, and 2010 as possible for each city). • Delineation steps: –– The boundaries for each of the cities were visually identified for three different dates circa 1990, 2000, and 2010 from satellite imagery. The satellite imagery was Landsat Thematic Mapper or Landsat Enhanced Thematic Mapper (depending on the year) imagery data. These imagery data have a 30-meter spatial resolution with seven multispectral bands. The date and type of imagery varied between the cities. Table A4.1 at the end of this Appendix has the exact date and type of imagery that was used in the analysis. Also, each city boundary was projected in the local Universal Transverse Mercator (WGS 84, UTM) projection. The UTM projection for each city is also listed in Table A4.1. –– Within the imagery, each built-up portion of the city (where buildings were visible) was identified and then a polygon was drawn around the visually identified area. The polygon was extended to areas that were within 1.5 kilometers of the neighboring area. Therefore, if a visually identified area of buildings had a gap between it and the next area went out over 1.5 kilometers, then these areas where not added to the city polygon. However if it was within 1.5 kilometers, then the area was included.