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4. CASE APPLICATION
The two application cases are slightly different in the
methodology adopted due to the difference of city extent.
4. 1 Chengdu City
The main objective of the project is to detect the base value
of city land up to each estate. Procedure used in the project
is the combination of sampling investigation and historical
data with the assistance of CLAS. First, find out the weight
of factor and element using Delphi method. Secondly,
calculate the effect value of each factor and element by "the
assessment method of grid coordinate integrated effect
value". Next, the determination of land class relies on "the
division method on the total effect value frequency" and "
the division on the sectional drawing of total effect value".
At last, the calculation of estate base value adopts the
estimate of differential profit, in combination with the
stripping of differential rent and surplus value, based on
land class. 5 !
During the procedure, the CLAS play an important role at
stages of effect value calculation of each factor, land grade
classification and final presentation.
4. 1. 1 Effect value calculation
The determination of effect value use the raster data
analysis procedure. Base map is on the scale of 1;15,000.
The map was segmented into a 60-by-70 raster image. The
total area evaluated is about 21262. 5 hectares, which
includes the built-up area and the near suburbs. Each cell
has an area of 5. 0625 hectares, which meets the
requirements of the National Regulations.
Digitize all the distribution maps of 28 elements, including
those of point, line and polygon. Key in the apposite effect
radius and the correction coefficient for road.
The calculation of effect value of each factor includes three
stages. First, calculate the effect value for 28 elements
respectively. Secondly, calculate the effect value of nine
factors from the result of elements. Finally, calculate the
grand total effect value by weighted sum.
Different algorithms to calculate the effect value of each
element are identical with point, line and polygon
respectively. The point element has an effect radius and the
effect value attenuates with linear or index correlation to the
distance from the point. The line element has an effect zone
which best fits the algorithms of buffering. The polygon
element has a difference between inside and outside. The
inner part of a polygon has a unified effect value. The outer
part of a polygon suits the similar algorithms for the point
element. Fig. 2 shows a typical algorithm to calculate effect
value of point factor in raster data set.
4. 1. 2 Determination of land class
The assistant tools for the determination of land class and
estate base value includes frequency drawing, sectional
drawing, and contour of the total effect value.
4. 1. 3 Output
The computer screen is the essential medium to show the
results of city land assessment. Except maps and images,
there are 2-D and 3-D histograms resulted from statistical
analysis.
4. 2 Dongsheng
The determination of estate base value was based on land
profit and trade price in the basic unit of land class. The
similar methods are used at the corresponding stage of land
assessment to Chengdu City. The methods include " the
Delphi method" for the estimate of effect value of each basic
unit, and "the division on the total effect value frequency"
and "the division on the sectional drawing of total effect
value" for the determination of land class.
The base map scale is 1:2500. The assessment area of the
town is about 924 hectares with a population of about 40,
000.
The application of CLAS in the land assessment of
Dongsheng mainly focuses on the management of resulted
information. The information includes a data base for each
estate value and the final assessment map. The final
thematic maps in the data base include land unit map,
estate base value map, land class map, and land sample
point map. The map projection routines for the
transformation between Guess-Craig and latitude/longitude
provide the basis for the match of maps from different
resources. Fig. 3 shows the operational flow and the final
system components for Dongsheng.
Read next pixel?
Y
Within effect
radius?
Compute/renew effect value
Fig. 2 Algorithm for effect value
calculation from point samples
5. FURTHER EXPANSIONS
The increasing demand from the land management
departments and organizations prompt the further expansion
of the software package to include modules to manage
estate and household information and build more
sophisticated legend/graphic library.
6. CONCLUSIONS
417
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
