26 In this case, with the assumption that deforestation in Period 1990
– 1997 will be non-forest in Period 1997 – 2001, since the image data 1997 will be the first date and image 2001 will be the second
date. Both images became one stacked image. By the reason, the deforestation class class number 12 will be clipped by all classes
of raster Period 1990 – 1997. Only class number 12 of Period 1997 – 2001 will be as input theme and Period 1990 – 1997 will
be as clip theme. This process is done by using Modeler Maker ERDAS Imagine 8.7
3.4.3. Vector Processing a Creating Cell Vector
, In this study as the nest for attribute data of each variables is cells. The cell is polygon with square shape,
with size 90 x 90 meters. These vector cells were created by
using ET Vector Grid, a plug in extension of ArcView 3.3. In its process, this tool just need four input extents points, Xmin, Xmax,
Ymin, and Ymax; and XY spacing or grid resolution 90 meters. The result of this process is a squared shape, which consist of cells
or grids.
Each cell has to be filled by either value 0 or 1 for independent
and dependent variables. Joining process to fill each cell, will be
easy by using ArcView Extension, Geoprocessing Assign data by location Spatial Join. The tool will join the ID of cell correlated
by either value 0 or 1, in an attribute table, and was saved by a
name Polygon VectorCell PVC. Name of PVC is based on
ArcView extension to create grid vector polygon, and to differ
with raster grid in this thesis, grid is changed to cell. The results
process are spatial and its attributes, that must be saved into a new
shapefile.
27
b Extracting Variables Data
In this research, dependent variable and independent variable will be list in Table 3.1.
Table 3.1. Binary data and categorization of variables as the factors of
deforestation
Variable Symbol
Value Category Variable
References
Unchanged Forest – Changed Forest
Y 0 Unchanged Forest –
Unchanged Non Forest Saadi, M. and R.
Abolfazi. 2003 1
Changed Forest Deforestation
Saadi, M. and R. Abolfazi. 2003
ElevationAltitude X
1
≥ 250 m Assumed
1 250 m
Assumed Aspect X
2
North and South Saadi, M. and R.
Abolfazi. 2003 1
East and West Saadi, M. and R.
Abolfazi. 2003 Distance from
population centers X
3
≥ 10 km Sitorus, J., E. Rustiadi,
M. Ardiansyah. 2001 1
10 km Sitorus, J., E. Rustiadi,
M. Ardiansyah. 2001 Distance from
Shoreline X
4
≥ 1 km Assumed
1 1 km
Assumed Slope X
5
≥ 25 - 90 degree Assumed
1 0 – 25 degree
Assumed Road X
6
≥ 1 km Assumed
1 1 km
Assumed River X
7
≥ 1 km Assumed
1 1 km
Assumed
Extracting vector data starts from obtaining the polygon that contains the attribute data such as contour data
≥ 250 meters and 250 meters. Sometimes this purpose needs editing manually of
using ArcView extension in order to make easy the process. The binary data must be put into the Polygon Vector Cell as attribute
data by using Assign data by location Spatial Join. It is done the same thing to other variables: road, river, distance from
population center, and distance from shoreline. Independent variable such as elevation was assumed that less than 250 meter
28 tends to occur deforestation. The references and research citation
is presented in Table 3.1. In ArcView 3.3, there is an extension Edit Tool 3.5, can
accommodate the purpose. There are three method to assign the data by location, i.e Inside attribute of polygon source must be
inside of the polygon target, Center Inside attribute of polygon source must be touched the center point of polygon target, and
Intersect attribute of polygon source must intersect to the polygon target. This tool is the same with Geoprocessing extension
Assign Data by Location. In order to anticipate over estimation of deforestation, the Inside
method is applied to this research. The process of extracting slope and aspect are different with
others. Extracting both features are using ArcView 3D Analyst for creating TIN from Features. The next process that uses grid
TIN is using ArcView ModelBuilder. ModelBuilder will identify input automatically of grid theme, in this case the result from
gridding TIN file. Extracting aspect from elevation grid file is provide default by
ArcView ModelBuilder. It will produce classification of aspect in raster or grid format that also as thematic or discrete grid theme;
with defined resolution 90 meters. The grid classes are: • 1 = Flat
• 2 = North • 3 =
Northeast • 4 = East
• 5 = Southeast • 6 = South
• 7 = Southwest • 8 = West
• 9 = Northwest
With the same procedure above, slope can be extracted. Slope is in degrees unit, meter for vertical unit and slope would be
classified into ten classes. • 1 = 0 – 5 degree
• 2 = 5 – 10 degree • 3 = 10 – 15 degree
• 4 = 15 – 20 degree • 5 = 20 – 25 degree
• 6 = 25 – 30 degree • 7 = 30 – 35 degree
• 8 = 35 – 40 degree • 9 = 40 – 45 degree
• 10 = 45 – 90 degree
3.4.4. Logistic Regression Model
