Census Mapping Using the GIS
System





Kobi Bahat
GIS Division

Tel. 972-2-655 3456
FAX 972-2-655 3531
e-mail: gis@cbs.gov.il



For the first time in the history of census-taking in Israel, it was decided to base
the geographic part of the 1995 Census on computerized mapping through the use
of the GIS, which enabled:
1. Detailed, up-to-date mapping of buildings in Israeli localities for the purpose
of creating complete coverage for census enumeration.
2. Production of maps of the enumeration areas (EA), which were functionally
suited to the work of the enumerator;
3. Linking census data (from the questionnaires) to buildings on the digital
maps. This enabled analysis of the census data at the building level, not
just at the statistical area level as with previous census polls.

The idea of using the GIS for the census came about at the end of the 1980s, but
the operative expression of this idea was realized only in the early 1990s. In
early 1993 a system was purchased for computerized mapping. At the same time,
we designed the mapping processes and we were ready to implement them. Due to
the limited time frame remaining before the start of the census, we implemented the
mapping process along two tracks:

The computerized mapping track: This mapping procedure was the main process
performed using the GIS. The computerized process was used to map 193 localities
whose population numbered more than 2,000 inhabitants, comprising a total of about
90% of the population of Israel. For these localities, some 6,000 EA maps were
produced.

The manual mapping track: Using the manual mapping procedure, 900 localities were
mapped whose population was less than 2,000 inhabitants, and for which about 900
EA maps were produced. An additional 300 EAs were produced for the
enumeration of those residents living outside the localities. EA maps that had been
produced using the manual mapping procedure were identical in their content and
characteristics to those maps produced using the computerized procedure, and the
details shown on the manual maps were also at the building level. This document,
however, will discuss only the computerized mapping procedure.

Organizational Framework of the Mapping Unit


Personnel
Mapping for the census was performed by a unit established within the CBS for
this purpose. Most of the people working in the unit did not have any prior
background in the field of computerized mapping, and they underwent on-the-job
training. At its peak, the unit had 40 workers, about half of whom were handling
computerized mapping, while the rest were handling manual mapping and other related
tasks.

Technical characteristics
The system purchased for the purpose of the mapping included Data General
hardware, with a server and four work stations.
Server: Aviion 8500 with 160 Mb of memory and 7 Mb worth of storage capacity.
Work stations: 17" NCD with 16 Mb of memory at the station.
Software: ARC/INFO (6) software.
Operating system: UNIX


Phases of the Computerized Mapping Process


The computerized mapping process included four phases:
1. Preparation of digital mapping.
2. Addition of addresses (street names and house numbers) to the maps.
3. Redistricting into EAs.
4. Production of GIS products:
addresses files for all localities;
EA maps, section maps and institutions' sections maps.

Phase A: Preparation of digital mapping

Because of the extent of the task and the professional aspects it entailed, digital
mapping was prepared for 193 localities by private mapping companies, with
supervision, direction and quality control carried out by the Survey of Israel, the
governmental mapping agency.
The mapping was prepared for all localities according to an identical specification
which was adapted to the needs of the census. The principle characteristics were:
Content:
a layer of buildings which included all the buildings within the boundaries of
the locality (which were larger than 2 meters).
a layer of "center-lines" for roads which included all the roads in the
locality, as well as the main dirt roads. Each section of road or street was
marked with data indicating the type and width of the road so that these
could be graphically expressed.
Technical characteristics:
The mapping procedure was photogrametric (from aerial photographs) on a 1:2,500
scale (resolution of 2 meters).
The maps were updated as of the end of 1992.
The mapping process took about one year. It should be noted that up to that point
in time, computerized mapping had never been undertaken on such a scale before in
Israel, and therefore, its progress faced a great many problems and difficulties.

Phase B: Addition of addresses

We added the addresses at the same time the mapping companies were progressing
with their tasks. We used two types of addresses:
recognizable, existing addresses in the 101 largest localities only. The
address components consisted of the street name and street code, house
number and entrance number. The street code is a single numerical code
for the entire locality, which enables single-value identification of the street.
This code also appears in the National Population Register.
synthetic addresses which we ascribed to buildings to enable their
identification. These addresses were used in the 92 other large localities
(which remained from the 193 localities from the computerized mapping) for
buildings that had no addresses, and for supplementing in those buildings
that did have addresses. The synthetic addresses were composed of:
unique street code in the locality; and a building code, unique in that street.

Addresses were added in three steps:
1. Preparation of addresses for input into the GIS:
Prior to entering the addresses, the map suppliers generated paper maps of the
computerized mapping they had done. On locality maps that included addresses, we
wrote those addresses that had been collected from different sources (primarily,
from the municipalities). We filled in what was missing using field surveys or
synthetic addresses.
We wrote the synthetic addresses on locality maps that had no addresses.
In addition, we indicated landmarks and institutions.
2. Loading the addresses file from the Population Register into the GIS:
Utilizing the addresses file from the Population Register was designed to save
keying actions and subsequent errors in the addresses input stage.
3. Input of the addresses into the GIS:
During the input process we transferred the addresses from the paper maps that
had been done during the preparation stage, to the digital maps that appeared on the
screen, with the help of the addresses file from the Population Register which
appeared in another window on the screen. The addresses were input in the
following stages:
1. Input of street names and their codes: First, the street names found in the
Register were input, then streets not found in the Register were keyed in,
and finally, the codes for the synthetic streets were keyed in.
2. Input of house numbers: This was done for each street separately, using a
method which was similar to the way the street names were input.
3. Input of landmarks and institutions.



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