6.1    Number of Rows and Columns within Raster

In the first attempt at performing the analysis it was very difficult to determine any locations, this was due to the number of rows and columns create when the vector layer was rasterized.  The number was determined by the desire to have a resolution of 20 meters.  This resolution required a raster of 1800 x 1800.  When evaluating the analysis output it become obvious that this resolution was too fine for the project,  especially since the project is an initial site selection.  Therefore, in the interest of producing a final map the was legible the number of rows and columns was reduced to 800 x 800.

This brings us back to the accuracy question again.  Since the resolution of the raster was reduced the accuracy of the analysis would decrease as well.  This would be due to the fact that each cell would represent a larger area, therefore edges of boundaries would be blurred.  This would not have been a major concern for the vegetation layer, since vegetation coverage does not follow strict boundaries.  However this would have affect the DEM layer, since this information was digitized from contours.  However, the accuracy of the project has been reduced on so many levels and the fact that the project was not a final cabin selection process the larger cell size was used in the analysis.
 

When the DEM was first created, the contour lines where digitized to the edge of the property boundary, since this was the area of interest.  However the vegetation layer was digitized to the edge of the study area, which was a large geographic area.  When these two layers were overlaid, IDRISI returned error messages.  The DEM needed to be recreated from a map that covered the same geographic area as the vegetation layer.

Being a user who was familiar with vector GIS packages, it never crossed my mind that the geographic area needed to be consistent throughout all layers.  It was fortunate that re-digitizing was possible, if that had not been the case, there is the possibility of changing the vegetation layer to match the DEM layer when the layer was rasterized.
 

Throughout the project accuracy is discussed in depth.  This is an important component to any GIS project, since accuracy can be affected at every turn of the project.  Therefore, before starting any project it is necessary to not only determine the data set accuracy but also ensure that there is an understanding of  how the analysis will affect result.

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