3.
Methodology
Cartographic
Weighted Linear Combination Model
Boolean Overlay Approach Model
In
order to use my data in Idrisis, Arcview was used to convert the file
format. There are several steps involved
to convert the data format from ArcInfo to Idrisis.
1. Import data into Arcview (export Data
Source à ASCII Raster)
2. Import data into Idrisis (File à Import à Software à Specific Format à ArcInfo raster ASCII format to Idrisis)
WLC Method
In
order to identify potential high landslide occurrence area, WLC method was
used. It is considered to be the
most effective method for this particular project since WLC is an averaging
technique that places my analysis exactly halfway between the AND (minimum) and
OR (maximum) operation.
To
use WLC method, fuzzy was used to rescale factors to a particular common range,
and to use the fuzzy factors with the MCE module, they should be standardized
to a byte-level range of 0 – 255.
Using the standardized continuous scale of susceptibility from 0 (the
least susceptible to landslide occurrence) to 255 (the most susceptible,)
likely areas for high landslide occurrence were predicted.
Weighting
factors for aggregation
The
advantage of this method is that it allows the ability to retain the
variability from the continuous factors.
Moreover, it gives ability to have factors
to trade off each other. In other
word, they indicate a factor¡¯s importance relatively to all other factors and
they control how factors will trade off for each other.
To
predict possible landslide area, I used nine factors and two constraints. The following is a table made using pairwise comparison
technique.
Boolean Method
Because
Boolean overlay method does not trade off, it had little flexibility. Also, it is a very conservative method
since Boolean MCE analysis is a logical AND (minimum) operation; thus locations
are considered suitable only when they exactly meet all criteria. In my work, Boolean overlay approach was
very effective since it predicted accurate locations of the most susceptible
area and no others with less susceptibility. To use Boolean overlay method, I set the area with low
landslide occurrence to 0 and the high to 1. I used nine factors, and they can be viewed in Cartographic
Boolean Model.