International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
(2) Graphic Generalization
Constraint 9 and 10 describe requirements and specifications of
the objective soil map. They are involved in the phrase of
preparation and preprocess, but also steer the solution of
graphic generalization. Take the solution for solving conflicts
caused by soil parcels smaller than the minimal area as example.
For Constraint 9, the sequence of appropriate operations for the
conflicts is enlargement, aggregation, amalgamation, collapse;
but for constraint 10, amalgamation, collapse is more
appropriate in terms of the efficiency of implementation. The
generic constraints govern the implementation of these
operators. For example, minimum size and self-intersection are
used to avoid invalid or incorrect geometric conflicts; shape/
angularity, size ratio, alignment/pattern and neighborhood
relations work for preserving the properties of soil distribution.
(3) Quality Evaluation
The generic and thematic constraints are used as the standards
in the evaluation of generalization results. The thematic
constraints mainly evaluate the quality of the result map from a
macro view of point, whereas the generic constraints focus on
the detailed aspects of geometric graphics.
= … Preparation and Preprocess
Thematic Constraints Generic Constraints
Constraint 1, Constraint 2 Minimum size,
Constraint 3, Constraint 4 Minimum distance,
Constraint 9, Constraint 10 Size ratio, Shape/Angularity,
Alignment/Pattern
Thematic Constraints Generic Constraints
Minimum size,
Minimum distance, Separation,
Self-intersection, Amalgamation,
Shape/Angularity, Size ratio,
Alignment/Pattern,
Neighborhood relations,
Spatial context, Aggregability,
Visual balance
Constraint 9
Constraint 10
Constraint 11
Constraint 12
Thematic Constraints Generic Constraints
Minimum size,
Minimum distance, Separation,
Self-intersection,
Shape/Angularity, Size ratio,
Alignment/Pattern,
Neighborhood relations,
Spatial context, Visual balance
Constraint 3
Constraint 4
Constraint 5
Constraint 6
Constraint 7
Constraint 9
Constraint 10
Figure 1 The Integration of Thematic Constraints with Generic
Constraints
4. IMPLEMENTATION OF SOIL MAP
GENERALIZATION
Section 2 investigates the main thematic constraints in different
phases of generalization process. Then section 3 analyzes the
relationship and integration between thematic constraints and
generic constraints. In this section, two special problems about
soil map generalization will be discussed to further illustrate the
importance of thematic constraints and the integration with
generic constraints.
(1) Transformation of soil category
Transformation of soil category is to transform soil categories
of soil parcels from the lower level to the higher one. We
employ Chinese Soil Taxonomy (CST) as the base of soil
mapping, in which the order from higher level to lower level is
soil order, soil suborder, soil group, soil subgroup, soil genus
and soil series, respectively.
- Generalization based on paper map: More than one
level of soil category are represented in many paper
maps to portray soil distribution (e.g. The Soil Atlas of
China 1986, The Land-resources Atlas of Beijing 1990, The
Atlas of The Changjiang River Basin 1999). For example,
the soil map (1:600000) in the Land-resources Atlas of
Beijing portrays soil group or subgroup by filling-color
method and marks numbers on each colored soil parcel to
distinguish different soil genus in a same soil group or
subgroup. The basic soil parcel represents soil genus. When
the map is used as the base map to produce a new map with
smaller scale, the category level of soil genus is neglected
and the soil parcels are merged: with their neighbouring
parcels which belong in the same soil group or subgroup. In
the final map, the basic soil parcel represents soil group or
subgroup.
- Generalization based on soil database: The strategy of
generalization varies with the different database. Zhang ef
al. (2003) introduces the soil classification coding system of
Chinese soil database at the scale of 1111000000. The soil
category can be encoded with 7 digitals. Soil order, soil
group and subgroup are represented by the first, the second
and the third digital respectively. And soil genus and the
code of soil profile are represented by the combination of
the fourth and fifth one, and the last two digitals
respectively. The format of soil category code contains
potentially the classification system of soil category.
Therefore, the soil category can be easily transformed from
higher category to lower one by omitting the latter digitals.
If soil database does not involve any classification system
of soil category, a classification system should be built first
based on the database and the purpose of the objective map.
Then the soil category can be transformed from lower level
to higher level according to Constraint 5, 6 and 7. After
generalization, the basic soil parcels in the derived database
represents the lower categories.
(2) Generalization of soil complex
Soil complex is a special representation in soil map. Therefore,
the generalization of soil complex is a special issue which is not
involved in the generalization of other kinds of data or maps.
The category transformation of soil complex has been discussed
in Constraint 8 in detail. There are two situations relate to soil
complex during the phrase of the graphic generalization. The
first one mentioned in Constraint 11 associates several simple
soil parcels into one new soil complex to solve graphic conflict.
The second situation is to solve the conflicts caused by the
present soil complex in the map or database. For example, one
soil complex is smaller than the minimal area. There are some
alternatives to deal with it. The first one is to associate the soil
complex with its neighbouring soil parcels into one new soil
complex with more soil categories if its neighbouring soil
parcels are also smaller than the minimal area. The second one
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