DATA PREPARATION AND MANIPULATION
I added the DEMs (using Spatial Analyst) and shapefiles into ArcView, and then clipped the themes to a manageable study area. For clipping the grid theme I used a script from http://arcscripts.esri.com, called ClipGrid. For the vector themes, I used the Geoprocessing Wizard.
One problem was that the attributes were coded in a way that was not meaningful to the user. I looked up the attribute meanings using BC Albers Tools, and their ODCB look-up tables. I then selected the themes that I could use for construction of the maps of the two study areas, most importantly, the theme that distinguished between wooded and non-wooded areas.
A fundamental problem with this was, that those were actually not areas, but line segments, because the data set covers all of the province and is cut at the mapsheet boundaries, resulting in open polylines. The same problem existed for all of the other data that should be in polygon shape, such as lakes, glaciers, etc. As a solution to this problem, I manually closed all the lines of all applicable themes with the vertex-editing tool at the edges of the clipping boundary. I then employed a FME Workbench scheme that turned the now closed polylines into polygons. If a line was not properly closed, a line file was also produced, indicating that not all lines had been closed yet, so corrections could be made subsequently.
What followed was manually assigning an attribute code for non-wooded and wooded areas to the polygons of the important vegetation theme, because the lines purely represented the boundaries of wooded and non-wooded areas. No information was being provided about the side (left or right) of the line that was wooded. The elevation information of the DEMs and the information of the other themes were helpful, and let me easily assign those attributes, e.g. high areas, lakes, marshes, braided streams, etc., are non-wooded. Also, I gathered topographic maps, and aerial photographs, and used those as interpretation aids in addition to my personal knowledge (hiking) of the two study areas. Examples:
Topographic map: Wapta Lake area
Orthophotos: Wapta Lake area 1 2
I added a theme for peaks, digitized the peaks for the study areas, named them, and assigned labels to them. Labels were also assigned to some lakes, highways and rivers.
The resulting ArcView maps of the two study areas (92 and 82) can be viewed here (click for magnification):
The topographic maps and aerial photographs were also of help for the following task: the most crucial task of all, defining the treeline. Fact is that actual treeline data is not available. Treelines are an averaged human construct of a certain altitude at which trees stop growing. The data that is available shows only wooded and non-wooded areas. The reason for an area being non-wooded is not stated. I could identify the following areas that must be excluded from the areas bordering the treeline:
- lakes
- landslides, talus slopes
- marshes
- braided streams
- any non-wooded low-lying areas
- moraines
- areas that were covered by glaciers in the past, and are now uncovered due to receding glaciers
- areas with extremely steep slopes
- logged areas (however: not applicable to these particular study areas, as they are park land)
The treeline is essentially equivalent to the average maximum elevation of the wooded area. I went back to the original lines-version of the vegetation layers, and deleted all vertexes of line segments that I decided do not affect the actual treeline. This was a very tedious process, and the result was a fragmented tree line at both study areas (click for magnification; 92 left, 82 right):
Subsequently, the climate data had to be analyzed. Essentially, I created an Excel-spreadsheet for the precipitation data, and calculated the average precipitation at desired stations. I entered the mean temperature values for the applicable months into another Excel-spreadsheet, and used this information, complimented with bioclimatic research, to make decisions about how to model the continuous surfaces for temperature and precipitation.
