ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
The algorithm for determining changes in the feature space
region between two time points is as follows:
[Step 1]
By setting T as system time and performing a feature space
search with P as the reference point for feature space D,
obtain a vector (V1) constituting the feature space region and
a connector (C1) representing the feature space region. Set
Q = C1. Set N = 1.
[Step 2]
By setting T' as system time and performing a feature space
search with Q as the reference point for feature space D,
obtain a vector (V2) constituting the feature space region and
a connector (C2) representing the feature space region.
[Step 3]
When V1 = V2 (all points are equal), Q'N = Q, R'N = 1, and
the procedure ends. Otherwise, proceed to Step 4.
[Step 4]
Compare V2 with V1, and partition V1 into a region included
in both V1 and V2 (Vc, which may be a set of multiple
polygons), and the part of feature space outside that region
(part included in V1 but not V2) (Va1 - Vak: a set of polygons).
Add Va1 - Vak to the list of Va.
[Step 5]
If Vc exists, set Q'N = Q and seek R'N, and house each point.
Set N = N+1.
[Step 6]
If Va exists, select one polygon Vat from the list of Va.
Generate a point inside Vat, set that point as Q, and return to
Step 2. If Va does not exist, the procedure ends.
6. Data utilized and strategy for data management^]
6.1. Data utilized and strategy for data management
Census data consists of base unit number and shape
information for base unit area, and base unit number is used as
a key to relate this data to total information (population, number
of households, etc.). The main shape information consists of
base unit area boundaries and the main attribute information
consists of base unit numbers and total information. We make
some proposals regarding the method of management using
DyMSIS/KIWI+ format.
(1) Base unit area boundary data
This data is managed as shape data using vectors. Base unit
area boundaries are revised after the previous census date,
and all revisions are completed prior to the current census date.
Accordingly, temporal factors for the base unit boundary
vectors are set as follows (Figure 6a):
GS: Date of data revision (in the case of initial data, date of
data creation)
GE: First census date after data revision date
ES: Date of data revision (for information that is not subject to
extinction, MAX value)
EE: First census date after data revision (for information that is
not subject to extinction, MAX value)
Further, feature spaces are defined as follows:
(1) Base unit area feature space
Area feature space defined using base unit area data (vector)
and base unit number data (connector).
(2) Total data feature space
Area feature space defined using base unit area data (vector)
and each item of total information data (connector). Defined in
accordance with total data type. For example, a population
statistic feature space is defined using population statistic
connectors.
Not Exist
►
1995.10.1 Revision Revision 2000.10.1
Date A Date B
Census Date
(a) T Factors for Base Unite Boundary
1995.
Exist
Total Result
Data in 1995
Not Exist
Exist
Total Result
Data in 2000
0.1
Not Exist
2000.10.1
Census Date
Census Date
(b) T Factors for Total Result
Figure 6. T Factors for Census Data
6.2. Revision of base unit area data
Base unit areas are revised with the census date. In the
following, revision of base unit areas is considered from the
viewpoint of data management (Figure 7).
(2) Base unit number data
This data is managed as representative points of areas using
connectors. Because base unit numbers, which are connector
elements, change with revision of base unit boundaries, the
method of setting temporal factors is the same as for base unit
boundary vectors.
(3) Total result data
This data is managed as representative points of areas using
connectors. Because total information changes every time a
census is conducted, the following temporal factors are set for
total census information (Figure 6b):
GS=GE: Census date
ES=EE: Day before next census date
(1) Merging of base unit areas
Two base unit areas are merged to form a single area. In data
management, the common boundary between two regions is
eliminated. In this case, the base unit numbers for the two base
unit areas are eliminated and a new base unit number is
generated.
(2) Division of a base unit area
One base unit area is divided into two areas. In data
management, a boundary line dividing two regions is
generated. In this case, the base units number for the original
base unit area is eliminated and new numbers are generated
for the two new unit areas.
