|
A Geographic Information
System is a computer based tool that allows the user
to draw upon stored data in order to identify spatial
relationships between graphic features, and to produce
maps drawn to suit a particular need. A well managed
GIS constitutes storing, manipulating, and displaying
spatial and relational data from a database. A spatial
and relational database respectively describes the
Graphic feature and the associated attributes.
GIS
Objectives
In order to make decisions
in the public interest backed by information to
achieve greater efficiency and community viability a
GIS is an essential link. Downey's Public Works
Department's majority of functions involve tasks
dealing with land or geographically related features.
To provide customers and citizen with an access to
computerized information and to help in departmental
decision making process, where the use of graphical
data such as tables, maps, plans and other graphic
documents is essential Department of Public Works has
initiated the process of bringing GIS online.
We welcome you to browse the site and be informed
about the GIS information on the City's web page and
learn more about City's Geographic Information
Systems.
FY
2000-2001 Targets
Basis
of GIS
Spatial data can be most
simply defined as information that describes the
distribution of things upon the surface of the earth.
In effect any information concerning the location,
shape of, and relationships among, geographic features
can be part of GIS databases.
Why invest in GIS?
In a long term planning
a GIS can provide the following benefits.
- Enhanced
productivity
- Apparent added
capability
- Capability to
respond to anticipated events
- Intangible benefits,
and
- Online presentation
of data.
Traditional
Data: Paper
based card indexes, asbuilt, and survey archives
(including paper based records, databases)
qualitative report texts and data on microfiche
archives, plots aerial photograph
interpretations which may include attribute data and
photo source information topological databases etc.
Components:
Most professionals agree there are five main
components in a GIS. This include Hardware, Software,
Data, Procedures and People. Data and People are the
most important component in a Geographic Information
System.
Basic
steps involved in a GIS are:
Analysis:
Geo-spatial analysis procedures perform analyses which
take into account sources of data and spatial
relationships between data items. A collection of
procedures are then, combine into GIS applications
which provide an efficient means of performing
effective geo-spatial analysis.
What Questions Can a
GIS Answer?
- Location:
"What is at..." Location can be
established in many ways, such as name,
latitude/longitude, traffic analysis zone
etc.
- Condition:
"Where is it?" This scenario helps to
find a location where certain conditions occur
(show all the water mains of size 10" or
greater, show all the parcels located adjacent to
the existing sewer line).
- Trends:
"What has changed since ...?" This
scenario helps to determe the trends in a
particular situation
- Patterns:
"What spatial patterns exists?" This
scenario determines whether there is a
relationship between traffic fatalities and
certain types of highway surfaces. It can also
identify anomalies and their spatial pattern.
- Modeling:
"What if ...?" This scenario
determines the merits of administrative decisions,
e.g., the relative cost of acquiring various
rights-of-way for a highway project or parcels
effected in case a water main is shut off, etc.
Different
from a cartographic map, a GIS will allow traditional
database queries to include the ability to analyze
data based on the different scenarios mentioned above.
For example, we may want to find all areas of
residential land effected by the broken water main.
This is a problem that a traditional database cannot
solve, for the reason that water line types and land
parcels divisions simply do not share the same
geography. Traditional database query is fine as long
as the attributes belong to the same categories. But
when the entities are different, the queries does not
work. A GIS allows to compare different pieces of
information based on their common geography and
guarantees an eventual process of integration and
sharing of databases.
GIS can be considered a decision support system.
Alternative outcomes of environmental phenomena can be
modeled and revised. Also, multiple databases can be
linked to geographic points on the ground. This can
include zoning, council districts, or utility
locations. The possibilities are numerous. Common
applications of GIS include utility management and
demographic profiling, managing urban resources and
development, image processing and digital
Ortho-Photography.
Output: The product of
GIS analysis is a set of processed data which can be
written in a list or converted to a chart in a printed
report. Typically, however, the resulting dataset from
performing GIS analysis is displayed graphically in
the form of maps. The key to GIS is the fact that the
maps themselves are not stored in the system, there
would be far too many of them. Instead, GIS processes
are stored allowing the user to run the process and
retrieve new data for each map request. Doing so
results in greater flexibility in customizing maps and
regular trips back to the original data insures that
the latest information available is being processed
and represented on the map.
Interactive
Maps
The input to a Geographic
Information System is a database query. The output is
information. The information which results from the
GIS query makes up a dataset which can be presented in
maps, tables or reports. Taking advantage of available
GIS and internet technology the Downey GIS website is
planning to offers the ability to submit a query,
produce a map of the City and display the map online.
The database is queried by selecting from a list of
features such as street centerlines, water, sewer or
storm drain utilities. Information about each feature
from the query result is placed in a separate graphic
layer. The layers are then combined and displayed
together to produce a custom map based on all the
features selected. The user will able to set map scale
and coverage area by zooming and panning in the
display window. The mapping features will be available
online for Flood zone, Water, Sewer, Storm Drain,
Street Center Line and Parcel Data.
Source
of GIS Data
Central to any Geographic
Information System is the data upon which it is built.
The data is supplied by individual departments whose
responsibility it is to produce and maintain accurate
data as part of conducting business daily within the
city.
The planned layers for the GIS databases are as:
|
Dataset
|
Department
|
Content
|
| Cadastral |
Public
Works |
Parcel
Boundaries |
| Planimetric
Features |
Planning |
Building
Footprints |
| Digital
Terrain Model(1' ft contour) |
Public
Works |
Topographic
Lines |
| Zoning |
Planning |
Citywide
Zoning |
| Street
Centerlines |
Public
Works |
Countywide
Street Centerline with Address Ranges |
| City
Limits |
Public
Works |
|
| School
Locations |
Planning |
Citywide |
| Fire
station locations |
Fire
Department |
Citywide |
| Neighborhood
Boundaries |
Planning |
Citywide |
| Utility
Layers (Water, Sewer, Storm Drain) |
Public
Works |
Same
coverage as planimetric data |
| Floodplains |
Public
Works |
Citywide
flood zone |
Rapid
access to high quality, computerized geographic
information data will improve the services. In Downey,
Department of Public Works is accelerating these
activities by fully implementing a comprehensive
geographic information system (GIS). DPW
encourage and guide the development of GIS to serve
both public and private sector applications. GIS group
is responsible for providing services which ensure the
quality of and access to these data. DPW manages the
GIS database to maximize data sharing and
compatibility between other departments, develops GIS
standards and guidelines, provides quality control
services, and maintains public "one-stop
shopping" for digital geographic data. GIS group
provides an array of application development and
technical services including the web publishing of GIS
data.
Online
GIS Layers
Currently we are in
the process of developing a number of maps in the
Downey area for on-line viewing.
For additional information or any inquiries, please
contact:
BY
TELEPHONE
Tel: (562) 622 - 6721
BY
FACSIMILE
Fax: (562) 904-7296
BY
MAIL
City of Downey
Public Works Department - GIS
P.O.Box 7016
Downey, CA 90241-7016
IN
PERSON
City of Downey
Public Works Department - GIS
11111 Brookshire Avenue
Downey, CA 90241-7016
|
