Establishment of the Census Geography in Taiwan 2

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Establishment of the Census Geography in Taiwan

Tsai, Bor-Wen1, Chen, Chin-Hong2, Shen, Jeremy3

1Associate Professor, Department of Geography, National Taiwan University,

[email protected], Department of Statistics, Ministry of the Interior, [email protected]

3Director, Information Center, Ministry of the Interior, [email protected]

Abstract

Census data is able to derive valuable information for government policy-making.

However, there was no dedicated system for census data in Taiwan. Data on

individual units (individual person/household) was aggregated by jurisdictional

units either in text form of digital format or in tabular form of report. Critical issues

are data aggregated by jurisdictional units is usually too large to provide detail

information on local area of interest and is difficult to illustrate spatial distribution

and variation.

This paper reports an establishment of census geography in Taiwan. It becomes a

part of national spatial data infrastructure of Taiwans National Geographic

Information System (NGIS). Census geography is a mechanism for census data

to be associated with spatial location explicitly. It implies the spatial allocation and

spatial aggregation of census data. A geo-referencing system for spatial allocation

and a hierarchical architecture of census geographic areas are evaluated and

designed. This architecture is able to provide spatial-explicit and detail information

for census data and is able to conform to the existing jurisdictional system as well.

The designed architecture comprises a statistical area and levels of dissemination

areas for data provision in terms of different level of detail. In addition to census

data, custom dissemination areas based on the identical statistical area are


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allowed to serve social-economic data provision such as crime or health data. The

statistical area is the basic unit for data aggregation. The major concerns are

protection of privacy and size of the unit in terms of spatial and attribute

consideration. The dissemination areas are units for data distribution. There are

four levels of detail for different applications. The evaluation of existing NGIS

database is also conducted to make best use of existing data for the

implementation of census geography.

Key words: Census Geography, Statistical Area, Dissemination Area

1. INTRODUCTION

Demographic data is critical information for government policy making. There are

two demographic data sources compiled and disseminated by government

agencies in Taiwan. One is the Population and Housing Census which is held by

the Directorate-General of Budget, Accounting and Statistics, Executive Yuan

every ten years. Another is the Census Register System which is a regular

household register system by the Department of Household Registration. Both

data on individual unit (household) was aggregated by jurisdictional areas either in

text form of digital format or in tabular form of report. It is therefore difficult to

illustrate spatial distribution or variation of social economic status. The

jurisdictional boundaries are subjected to change when the population of

jurisdiction increases or decreases to a certain level. There were 585 village (the

smallest jurisdictional unit in Taiwan) boundaries be modified between 1998-2007.

Users of census data who wish to compare statistics between different

geographical areas, or for a particular area between different points in time, need

to be able to identify and understand the area to which the data refers. Another

problem encountered is that data aggregated by jurisdictional units is usually too

large to provide detail information on local area of interest. The average

population size of villages is about 3000. It is difficult to grasp detailed information

for such large aggregation unit. The census data become less useful in


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large-scale planning or decision-making tasks. Comparing to most modern

countries in the world, there are many dedicated census system such as the US

TIGER system (Topologically Integrated Geographic Encoding and

Referencing)(Broome, 1984). the SGC system (Standard Geographical

Classification) of Canada (Canada's National Statistical Agency, 2007a, 2007b,

2007c, 2007d, 2007e, 2007f)the ASGC (The Australian Standard Geographical

Classification) of Australia (Edwards, 2001, Puall, 2003), the

of Japan (http://nlftp.mlit.go.jp/isj/index.html ) and so on. A census geography

was established to serve as a dedicated and spatial-explicit census system. It hasbecome a part of national spatial data infrastructure of Taiwans National

Geographic Information System (NGIS).

2. CENSUS GEOGRAPHY

Census geography is a mechanism for census data to be associated with spatial

location explicitly. It implies the spatial allocation and spatial aggregation of

census data. The NGIS has established a GIS database for building addresses.

The address geocoding is utilized to allocate each individual data to its associated

spatial unit. Once the individual data has been geo-referenced, spatial

aggregation can be done by the desired areas from the finest boundary to the

most generalized boundary. Information can be derived in different detailed levels

as needed. A hierarchical aggregation system is employed. The designed

architecture comprises a statistical areaand six levels of dissemination areas

for data provision in terms of different level of detail (Figure 1). In order to conform

to the existing jurisdictional system, the third level dissemination areas are

consistent with the existing township boundaries and the fourth level is consistent

with the county boundary. In addition to census data, custom dissemination areas

based on the identical statistical area are allowed to serve social-economic data

provision such as crime or health data. The custom dissemination areas can be

conformed to the existing system at whatever appropriate level (Tsai, et al. 2008).


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Figure 1 Architecture of the Designed Census Geography System

The statistical areas are basic units for data aggregation. The major concerns are

protection of privacy and size of the unit in terms of spatial and attribute

consideration. The dissemination areas are units for data distribution. In addition

to privacy consideration, provision of different levels of detail for different users is

the major concern.

6th level disseminationarea (nation)

5th level disseminationarea (regional planning)

4th

level dissemination area (county)

3rd level dissemination area (township)

2nd level dissemination area

1st level dissemination area

statistical area

custom dissemination area

-- handicap data

-- business data

-- health data

-- crime data

--


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3. ESTABLISHMENT OF THE CENSUS GEOGRAPHYU SYSTEM

A preliminary study was conducted by a research team of National Taiwan

University to set up the criteria and rules for building the census geography

system. The considerations of boundaries for statistical and dissemination areas

are as follows.

Boundaries of any unit must be visible and stable in the field as possible

Consequently, the road network and drainage network are the best candidates forboundaries. Ridge lines are supplementary boundaries in rural or mountain areas.

Homogeneous distribution in each unit

Distribution of data in each unit should be homogeneous as possible. Household

register data is employed to examine homogeneity of population and household.

The household register data is maintained and updated by the Ministry of Interior

nationwide routinely. This data contains individual household information with

address embedded. GIS address matching method was employed to locate every

household (Figure 2). The homogeneity of each proposed unit can be examined

visually or by GIS point pattern analysis.

Figure 2 Distribu tion of Households


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Consideration of privacy invasion

Privacy is the major concern for the system. After careful examination of the

distribution of population in Taiwan, we set the lower and upper limits of

population size for the statistical, 1stand 2nddissemination areas respectively. The

upper limit for the statistical areas is 450 persons. The lower limit for the 1 st

dissemination is 100 persons or 40 households to protect privacy and 1000

persons for the upper limit. The upper limit for the 2nddissemination areas is 3000

persons.

Utilization of available data as possibleMust efforts including time and budget are needed to build the census geography

system from scratch. Fortunately, many GIS databases have been established by

the promotion of the Taiwan NSDI (NGIS) for the past 20 years. There are

different sources for road network. The Ministry of Transportation and

Communication has built a GIS database for road network with road width greater

than 6 meters. However, there are many streets with road width less than 6

meters in urban areas. Those streets can be extracted from 1/1000 digital

topographic maps that are available for most urbanized areas in Taiwan. GIS

drainage and watershed databases are constructed by the Water Resource

Agency. Ridge lines can be derived from 40 or 5 meter DEM constructed by the

Ministry of Interior.

Shape of units should be compact as possib le

Narrow and long shape units are not preferred. This requirement can be

confirmed by GIS shape analysis.

The designed system should conform to the exist ing system

The existing system uses jurisdictional boundaries for data aggregation. The

designed system adopts jurisdictional boundaries as high level dissemination

areas and add three levels of aggregation units (the statistical area, 1stand 2nd

dissemination areas) to increase detail of data.

Ensure boundary stability

The designed system replaces the village boundaries with three levels of

aggregation units. The reason of discarding the village boundaries is its frequent


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boundaries revision. It is difficult to do time series analysis if the boundaries of

aggregation units are changed frequently. Table 1 shows the village boundary

revision from 1995 to 2008. Figure 3 shows change of village boundaries between

1990 and 2004 of Zhuangwei Township in Yilan County. It is obvious that the

village boundaries are subject to change frequently.

Table 1 Summary of Village Boundaries Revision

Year Name Changed New VillagesDisappear Villages

(merged or name changed)1995 34 0 0

1996 21 0 0

1997 13 189 3

1998 0 4 0

1999 9 1 0

2000 6 4 0

2001 0 15 0

2002 0 191 1572003 3 0 0

2004 0 39 40

2005 1 5 2

2006 2 61 43

2007 0 0 2

2008 3 0 0


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Figure 3 Village Boundaries of Zhuangwei Township in 1990 and 2004

4. RESULT

16 out of 22 counties have completed the establishment of the census geography

system. It took three years and cost US$ 1.25 million approximately. It is expected

to complete the whole work by the end of 2002.

Figure 4 shows the census geography system of Kaohsiung City. There are 6884

statistical areas, 4446 1st level dissemination areas, 698 2nd level dissemination

areas and 11 3rdlevel disseminations (the existing townships jurisdictional areas).

A case study was done by the NTU research team to demonstrate the rationality

and suitability of the census geography system. The project analyzed the Dengue

Fever cases that were held in Kaohsiung City and nearby areas of Kaohsiung

County in 2002. Cases were aggregated by statistical areas and 1 stand 2ndlevel

dissemination areas. Results of the census geography system and the original

jurisdictional areas were compared. Figure 5 is the distribution of individual

Dengue Fever cases. Figure 6 shows results of different aggregation units. It can

be seen that the census geography system is able to represent different levels of

detail. Data aggregated by the statistical areas represents the most similar


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distribution pattern with the individual cases. Data aggregated by townships

generalizes distribution information and exaggerates the hot spot locates at the

center of the study area.

Figure 4 the Census Geography System of Kaohsiung City

Figure 5 Distribution of Dengue Fever Cases, 2002


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Figure 6 Data Aggregated by Different Units

5. SUMMARY AND FUTURE WORK

It is concededly that census geography benefit to many social studies. Chu, et al.

(1990) reviewed the use of 1980 census data in Taiwan. They concluded that one

of the impediments in using census data is the inappropriate aggregation unit

(used to be the jurisdictional areas). The census or other activity data now can be

aggregated in a smaller unit, implying reduction of lost information due to

generalization by aggregation. Moreover, the aggregated data can be easily

integrated with the jurisdictional areas which are the aggregation units for some

social-economic data.


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Geocoding is the key issue for data to be integrated. Address matching is the

most common case for geocoding. Fortunately, Taiwans NSDI has established

the GIS address database for the entire country. Consequently, database

updating becomes the critical issue for the census geography system. A

procedure for GIS address updating is under developing.

Population and social economic data used to be integrated by jurisdictional areas.

People are accustomed to use this data for a long time. The utilization of census

geography system must be promoted. More applications should be demonstratedand disseminated.

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Establishment of the Census Geography in Taiwan 2