3.7 Generation of Decision Maps 
Once the GIS has analyzed the data based on 
the criteria stated above, the 
corresponding decision maps can be 
generated using a plotter or printer. The 
design of these outputs can be made 
directly onto the computer, and the 
generated maps are already in their final 
form. 
The procedure just discussed follows very 
closely the operations diagram of the GIS 
Application Development Division of NAMRIA 
which is shown in Figure 2. 
4. DISCUSSION OF RESULTS 
Li Suitability M £ Tul B 
Figure 3 shows the Suitability Map of the 
town of Tuba in Benguet province. Three 
(3) classes of suitability to agriculture 
are shown: high, moderate and low. 
Areas identified as highly suitable 
generally have slopes less than 25%. These 
have a total area of 1,255 hectares or 
about 3.50% of the municipality. Areas 
identified as moderately suitable generally 
have slopes less than 40%. These cover 
about 2,349 hectares or approximately 6.71% 
of the town. 
Together, these two (2) suitability classes 
are characterized by proximity to roads, 
and medium to low susceptibility to soil 
erosion/degradation. The rest of the town, 
comprising of about 31,428 hectares were 
classified as not suited to agriculture 
mainly due to their steep or very steep 
slopes. 
Suitability maps of mountainous areas such 
as Tuba are very important in the 
management of sloping lands in the country 
since Philippine law, in general, prohibits 
the use for agriculture of areas having 
slopes greater than 18%. However, if there 
are strong justifications for reclassifying 
these areas, such as those presented by 
suitability maps, then they can be 
"released" officially to the recommended 
land use. 
4.2 Soil Erosion Susceptibility Map of 
= 1 : 
Ene AE Pu Rene in 
Figure 4 shows the Soil Erosion 
Susceptibility Map of the Tamlang River 
Catchment in the town of Brooke's Point, in 
the island of Palawan. Three (3) classes 
of soil erosion susceptibility are shown: 
slight, medium and high. 
The areas identified as highly susceptible 
to erosion are generally open and denuded 
steep forestlands, with naturally occurring 
landslides. The soil loss within these 
sites are predicted at about 105 - 264 tons 
per acre per year. About 269 hectares or 
2.3% of the catchment area fall under this 
category. 
Areas classified as medially susceptible to 
erosion are also composed of steep 
forestlands, but are adequately covered 
784 
with natural vegetation. The soil loss in 
this category is predicted to be between 56 
— 96 tons per acre per year, encompassing 
about 444 hectares or 3.9% of the catchment 
area. 
The rest of the basin is predicted to have 
slight erosion of about 1 - 49 tons per 
acre per year. This is true for 93.8X of 
the catchment or about 10,767 hectares. 
Soil erosion is a major environmental 
concern in the Philippines, as this 
contributes heavily to the degradation of 
the precious agricultural lands. Soil 
erosion susceptibility maps provide 
valuable information that can guide the 
establishment of soil conservation measures 
and other related activities. 
4.3 Photo-based Tax Map of San Isidro. 
Bulan. Sorsogon. 
Figure 5 shows the photo-based Tax Map of 
a section of the village of San Isidro, in 
the town of Bulan, province of Sorsogon. 
The map presents information on property 
identification, boundaries and ownership. 
Figure 6, on the other hand, shows the 
property index map (PIM) of the same site. 
This map forms part of the official records 
of the Municipal Assessor's Office of the 
town, and is used as the basis for tax 
assessment. Information on this map is 
based on the cadastral survey of the 
village undertaken two (2) years prior to 
this study. 
Comparing the two (2) maps resulted to the 
following observations: 
a. there are major changes in property 
boundaries and corresponding lot 
areas; 
b. there are changes in ownership; and 
c. due to (a) and (b) above, revisions 
in their official land records and 
tax assessments are necessary. 
Thus, for the purpose of real property tax 
valuation, boundary maps based on rectified 
aerial photographs are indeed very useful 
especially in the absence of updated land 
survey records. In rural areas in the 
country, a systematic and accurate means of 
maintaining land records is vital to the 
prevention of social unrest, since land is 
the single most valuable property of the 
peasantry. 
5. CONCLUSION 
The foregoing discussions have presented 
only the initial studies conducted by the 
GIS Applications Development Division of 
NAMRIA in utilizing GIS and remote sensing 
to address current national concerns in 
land assessment. Other projects dealing 
with relevant issues in the environment and 
natural resources, such as flood risk 
assessment and the establishment of 3- 
dimensional resource information databases 
are earmarked for implementation in 1993. 
For the current year 1992, NAMRIA continued