Project Completed for: Advanced GIS Course | Spring 2015
To better understand the coverage of current cell towers and the potential to add more, this study looked at Los Angeles county and utilized ArcMap 10.2.2’s visibility analysis capabilities.
First, data was gathered, including the two main layers: a DEM of LA County and current cell tower locations. In ArcMap, the DEMs were converted to one raster layer using the Mosaic to Raster tool, with 32-bit float pixel type and one band.
The DEM and cell tower layers were thenclipped to fit the county boundary layer.
Several columns were added to the cell tower point layer: RADIUS0, RADIUS1, RADIUS2, OFFSETA, OBSELVA, and OBSELVB, where RADIUS0-3 equaled 0, 30,000, and 35,000 m, respectively, OFFSETA was set equal to average human height, OBSELVA equaled the total structure height plus the elevation at that point, and OBSELVB equaled the total structure height plus the elevation at that point plus 10 m.
Several columns were added to the cell tower point layer: RADIUS0, RADIUS1, RADIUS2, OFFSETA, OBSELVA, and OBSELVB, where RADIUS0-3 equaled 0, 30,000, and 35,000 m, respectively, OFFSETA was set equal to average human height, OBSELVA equaled the total structure height plus the elevation at that point, and OBSELVB equaled the total structure height plus the elevation at that point plus 10 m.
Three visibility analyses were conducted using a combination of this information. The visibility tool outputs raster layers, so four new raster layers were then converted to polygon layers. These new feature classes were then cleaned up by dissolving the polygons inside, so that all that remained were nine polygons in each layer (each representing the frequency of visibility).
Spatial statistics were conducted for each visibility layer, providing information on the total area that was “visible” (in our case, “covered by cell towers”) and “not visible” (“not covered by cell towers”). Percentages of LA County that are covered by towers were calculated based on the formula: 𝑇𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎 𝑛𝑜𝑡 𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝑏𝑦 𝑐𝑒𝑙𝑙 𝑡𝑜𝑤𝑒𝑟𝑠/𝐿𝐴 𝐶𝑜𝑢𝑛𝑡𝑦 𝑡𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎.
For the last visibility analysis conducted, three additional cell towers needed to be added at optimal locations. These optimal locations were determined using a LA County major cities point layer and a LA County roads line layer. Cities were categorized by population size and roads were categorized based on freeways and highways. Using these two metrics, three new cell tower locations were proposed, added by using the Editor tool.
Attributes for these towers were added, with their total structure height being an average of cell tower heights in LA County (36m) and their elevation at that point identified by an online source. Again, after visibility analysis was conducted, the raster was converted to a polygon layer, dissolved, and analyzed for basic stats.
