GIS & Mapping
General Information
What is GIS?
History
Real Estate
Mapping
Map
Gallary
Links- GIS and data links
Brian Knudtson, GIS Coordinator
Mahaska County Courthouse
Basement, SE Corner
106 South 1st Street
Oskaloosa, Iowa 52577
Phone: (641) 673-1454
E-Mail: gis@mahaskacounty.org
Hours 8:00 A.M. to 4:30 P.M., Monday thru Friday
General Information
The GIS Department was created in July 1999 to serve
the GIS needs of Mahaska County. My goal is to help
increase the efficiency and productivity of Mahaska
County through the implementation of GIS applications
and technology. The GIS Department maintains a large
database of digital mapping layers covering the entire
county. In Mahaska County's Geographic Information
System, features such as parcels, municipal boundaries,
hydrology, roads, bridges, and recreation areas are
represented as map features which are linked to a
database containing certain essential information.
GIS is used by several county departments, such as
the Assessor, Auditor, Engineer, and Environmental
Services. The GIS Department maintains equipment,
software and data, and produces hardcopy maps to support
the use of GIS by county agencies. The GIS Department
also manages the sale of mapping products and GIS
data for private and public users.
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What is GIS?
A Geographical Information System (GIS) is an organized
collection of computer hardware, software, geographic
data, and personnel designed to efficiently capture,
store, update, manipulate, analyze, and display all
forms of geographically referenced information. Simply
put, a GIS combines layers of information about a
place to give you a better understanding of that place.
What layers of information you combine depends on
your purpose - finding the best location for a new
store, analyzing environmental damage, viewing similar
crimes in a city to detect a pattern, and so on.
A complete GIS requires 5
components:
- hardware
- software
- data
- people
- training to interpret changes over time and space.
Unlike a paper map, where "what you see is what you
get", a GIS map can combine many layers of information.
Although the end product is often a paper map, GIS
allows dynamic changes to be visible and has the ability
to combine data from several different sources.
As on a paper map, a digital map created by GIS will
have dots, or points, that represent features such
as cities; lines that represent features such as roads,
and small areas, or polygons, that represent features
such as lake. The difference is that this information
comes from a database and has information attached
to it. The database stores where the point is located,
how long the road is, and even how many square miles
a lake occupies. Each of these features is stored
in a separate layer, which can be made visible or
invisible.
GIS can be subdivided into tow major types: raster
and vector. Raster packages, such as GRASS and Idrisi,
are pixel based. Applications that raster systems
are good for are surface modeling and viewshed analysis.
This color Landsat Imagery shows how the individual
pixels are visible as tiny squares. A vector package
such as ESRI's ARCInfo is based on the model of discrete
entities (i.e., points, lines, and polygons) with
connections to relational databases.
Each type of data format has its advantages and disadvantages.
Raster data accommodates continuous data, such as
topography, as is compatible with other data collection
and manipulation software such as remote sensing.
However, raster files are often very large and take
a long time to process. Vector data requires less
storage space and tend to have higher graphics, but
they do not allow you to produce the same kind of
modeling and "map algebra" functions as are provided
by raster data sets.
Why is layering so important?
The power of a GIS over paper maps is your ability to
select the information you need to see according to
what goal you are trying to achieve. A business person
try to map customers in a particular town will want
to see a very different information than a water engineer
who wants to see the water pipelines for the same town.
Both may start with a common map -- a street and neighborhood
map of the town -- but the information they add to the
map will differ.
What is a GIS Database?
A database is a logical collection of interrelated information
related to a particular subject or purpose, which is
managed and stored as a unit. A GIS database includes
information and data for spatial features as they relate
to location and shapes of features recorded as points,
lines, polygons, pixels, and grids and the descriptive
information stored as attributes for those features.
The data associated with the highlighted polygon
is shown in the table also highlighted.
More Information?
GIS is a dynamic and technically varied field. The
topics discussed on this page are just the beginning.
For more information, check out the numerous GIS websites
listed here, or search for "GIS" in your favorite
search engine.
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History
This website is the result of years of cooperation
between the various
offices and departments in Mahaska County. Below is
a short history of
the project.
In 1994, the Assessor's Office commissioned ProMap
Corporation of
Ames, IA to develop a Geographic Information System
to automate and
improve agricultural land valuation. In 1998 and 1999
additional
cadastral and photographic layers were added to the
geo-database and the
following departments were encouraged to participate:
Auditor, E911, and
Engineer. Soon after, the Information Technology board
was established
and Jon Lubke was hired as the County's GIS Coordinator.
In 2001 the
"MAGIC" website was developed in cooperation
with ProMap to deliver the
following types of public information via the World
Wide Web: Real
Estate -Mapping, Property Assessment, and Tax Administration.
This site
is continually being updated and improved to serve
the citizens of
Mahaska County. Send your comments to gis@mahaskacounty.org
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