Lab 6

First Arithmetic Model:

[Reclass of Coverclass] + [Reclass of sl_dist] + [Reclass of Slope of elevation] + [Reclass of Soildrain] + [Reclass of Stream Buffers]

First Weighted Model:

(([Reclass of Soildrain] * .3) + ([Reclass of Slope of elevation] * .3) + ([Reclass of Stream Buffers] * .2) + ([Reclass of Coverclass] * .1) + ([Reclass of sl_dist] * .1)) * 5

Data: Vegetation type, slope of elevation, soil drainage data, and stream buffers.
Purpose: Used as a landfill development suitability analysis for the area in concern. 
Cell Size: 1000, 1000
Measurement Units: Meters
Geographic Extent: Gallatin County, Montana
Date Run: 02/13/11
Model Run For: Yongwei Sheng/Kettleman City Officials

This lab was a raster data spatial analysis exercise. I learned how to create, convert, and do spatial analysis on raster cells. Such skills have enhanced my ability to use GIS as a valuable tool for problem solving and decision-making.

I began this exercise in spatial analysis by defining the vector layer outlining the fictional county as an ‘analysis mask’. This ensured that the suitability analysis would be calculated based only on data from the county in concern.

Next I derived a layer representing the slope of elevation from a DEM of the county. Such a layer is useful for determining an area’s suitability for excavation.

Another issue to consider may be proximity to other areas of concern. In regard to landfill development, it is important to consider a new site’s proximity to nearby streams and other already existing landfills. A buffer is the tool for solving this issue. Here I created a buffer layer with four one-kilometer rings surrounding the rivers in the county.

This vector layer was then converted to a raster grid for spatial analysis. The resulting grid was a floating point grid representing the continuous elevation data. For ease of analysis, I converted this from a floating grid to an integer grid.

To determine the location of nearby existing landfills, I selected from the attribute table all of the area’s landfills that are currently open. I then made a new raster layer with grid values representing meters from any given point to the nearest open landfill.

After adding two additional raster grids describing the area’s soil and vegetation type, my data consisted of 5 layers representing 5 concerns to consider in a landfill development suitability analysis:
1) slope of elevation, 2) proximity to streams, 3) proximity to already operating landfills, 4) soil drainage, and 5) vegetation type.

The raster data in each cell of these five grids was then reclassified to create five new layers, each with cell values based on a scale of only 1-5. Each of these grid layers was assigned a particular weight based on their relative importance to this suitability analysis.

Then, using the raster calculator, the weighted values of each cell of each layer were combined. The resulting layer was reclassified to produce a final suitability layer. Each cell of this final grid considers each of the five weighted criteria and has a value of 1-5, 1 being the least suitable and 5 being the most suitable site for a landfill.

I have used these techniques to show which parts of a fictional area of Montana are the most suitable for a new landfill. But these spatial analysis techniques could also be used to solve numerous other suitability issues in land use pertaining to private and commercial real estate development, business expansion and location, resource allocation, city planning, etc.

These same techniques could be used to help solve the debate over the expansion of a landfill in California’s Central Valley. In addition to determining which areas are most suitable for expanding the landfill, these tools could also help determine whether or not the existing landfill is the cause of several contaminations and heath issues.

A buffer around vector layers locating aquifers, wells, streams, springs and other sources of water would tell if areas of the landfill were already close enough to these sources to contaminate them. A slope of elevation raster grid would help determine how contaminates are expected to spread from the landfill. And a raster grid representing the area’s soil drainage data would help determine if contaminants are draining down to groundwater below.

By using these techniques, investigators would know how close the landfill is to sources of water, how the contaminants flow from the landfill, and whether or not contaminants are draining down into groundwater. This would help enable them to determine whether or not the existing landfill is responsible for the current heath issues.