Redistricting Enumeration Areas
and

Defining the Organizational
Structure



Rinat Calvo
GIS Division

Tel. 972-2-655 3545
FAX 972-2-655 3531
e-mail: gis@cbs.gov.il


The redistricting of the enumeration areas (EA) and their reorganization into
supervisory units (sections) was divided into five main phases:

1. Creating city block's layer - A "natural" city block is a group of houses
bordered by four streets.

2. Establishing the boundaries of the polling areas (updated as of the 1992
Knesset elections): The polling areas contain around 600 residents who are eligible
to vote. They are defined each year according to the population as it appears in
the Population Register. They are automatically created in the GIS as aggregates of
Register addresses and they are corrected by:
ascription / transfer of city blocks by linking the correct polling area
number to the city block;
digitization of new lines when the boundary of the polling area passed
directly between houses rather than along the street.

3. Building statistical areas as established in 1983 census was achieved by
aggregating several polling areas. Statistical areas always include complete polling
areas. At the end of this action, a layer of statistical areas was created.

4. Clipping the database into sub-regions was achieved based on the aggregate
statistical areas (about 12,000 households). This redistricting was done in the large
localities in conjunction with the organizational framework of the census. It enabled
the system shorter reaction-time.

5. Redistricting the enumeration areas: Redistricting of the EAs was designed to
create enumeration packets that will be equal in population size for all the
enumerators, so the workload would be balanced and manageable in order to be
completed within the allotted time frame. In the urban localities, an enumeration
packet was set at about 275 households. Accordingly, the redistricting process for
EAs was implemented in the following steps:
1. The work framework was prepared within the boundaries of the locality, or
within a sub-region for larger localities (sub-region is a supervisor's
control unit). Each statistical area was handled separately.
2. A statistical area displayed on the screen was selected as an aggregate of
several polling areas: Each polling area had, as previously mentioned,
about 600 eligible voters, and this was the closest to the desired size
defined for an enumeration area. As a basis for the redistricting, the
streets, city blocks, polling area layer and their numbers, and the population
size were displayed.
3. Generation of a preliminary EA redistricting report; The report analyzed,
for a selected statistical area, the population in each polling area, based on
the data from the Population Register, and showed:
The estimated population size and average number of persons per
household (data supplied by Demography Division in the ICBS).
the number of polling areas that existed, compared with the number of EAs
required;
the population of each polling area, compared with the population needed in
the enumeration area. If the population in the polling area did not come
close ( 10%) to the population in the enumeration area, the report showed the
number of people needed to be removed or added in the polling area in
order to make it an enumeration area with 275 households (translating the
population into numbers of households was done by means of a suitable
algorithm).
4. Turning polling areas into enumeration areas: According to the data from
the report, groups of houses were added or subtracted in those polling
areas that had to be made to match the size of the EA. This was done by
copying city blocks from polling area to polling area. A "natural" city block
is a group of houses bordered by streets, with its population size displayed
in the center.
Artificial city blocks can also be created digitally if the natural city blocks
are either larger or smaller than necessary, for the purpose of transfer
to a different polling area. This process was done for all the polling
areas in the statistical area, and in the final stage, all the polling areas
became EAs.
5. Producing the final EA redistricting report and correcting EAs: In order
to insure that the redistricting process was properly implemented, an
additional "EA Redistricting Report" was generated, identical in its format to
the initial report, which included a list of the EAs that had been created
from the polling areas. If redistricting was properly carried out, the
report indicated that the population size in the EAs matched the desirable
population size. If the redistricting was not carried out properly, the report
indicated those polling areas that still did not match the EAs, and the number
of people that still needed to be transferred.
Accordingly, the process of changing polling areas into EAs (as described
above) was carried out one more time. This process was iterative, until the
redistricting report showed that the process of correctly redistricting the
EAs had been completed. At the end of the process, a layer of EAs is
created for each sub-region/locality, and every EA is assigned a
preliminary number.
6. Unique Eas, such as institutions or industrial zones, were created at the
same time, but at pre-defined locations.

6. Ascribing enumeration areas in a sub-region to sections: This process was also
helped by the report which took into account the size of the EAs and the total
population in each sub-region. The report details the number of recommended EAs
in the section and the recommended number of sections in each sub-region/locality.
The adding of EAs to sections was guided by the report and by considerations of
geographic homogeneity. During the process of ascribing the EAs to sections, the
final number of the EA was also defined (sub-region, section and EA).

7. At the end of the redistricting process a GIS addresses file was generated for
each locality. All the necessary parameters for census identification were added to
each address record - statistical area, sub-region, section, enumeration area,
coordinates, unique identification number of the building to which the address
belongs, and additional data form the Register.



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