Land Use Change Analysis in Logan, UT using GIS
by Paul Morgan
and
Helen Kenyon-Bares
Introduction
Local and regional governments have increasingly seen the benefits of technology in executing many of their responsibilities. Computers have obviously changed the way most agencies do business. The processing, analytical and data storage capabilities of computers have given public agencies that have invested in such systems a great tool for accomplishing their duties. One example of how technology has changed the way governments do business is the development of Geographic Information Systems (GIS). The ability of GIS to store, manage and manipulate large amounts of spatial data, provides urban managers with a powerful tool. GIS's ability to link tabular, non-spatial data to locational information is likewise a powerful analytic capability. Many different facets of government use GIS technology. GIS also provides ways of viewing and analyzing data that was previously impossible or impractical. Federal and State level agencies can map large scale inventories such as soils, animal species and broad demographic information. By using various map layers, relationships between items such as precipitation, soil type and erosion can be studied. Though this information is useful at a macro-level, to many smaller entities, the map resolution and data are too broad to be applied at a county or city level. Whereas at the state level, property values may be represented by a county wide average, at the county level, an assessor's office needs to know an assessment value for each piece of property. Similarly, a city public works department needs information about water and sewer lines at a micro-scale level. With the aid of a GIS, a local planning and community development office can track zoning and site design plans that help form and shape a city.
An important part of the urban environment is how land is being used. When land use is discussed in an urban context, it generally refers to which human activity, usually economic, is being conducted on a given piece of property. Most schemes categorize land use into residential, commercial, agricultural and industrial divisions. Further distinction in the categories can range from a separation between light, medium and heavy industry to specific uses such as meat packaging or clothes manufacturing plants.
Many local governments maintain land use information either on hard copy maps or in
computerized databases such as Assessor's files. With GIS's ability to store and link data,
it has become a popular database for land use information. Many land use applications
integrate both GIS and remote sensing (RS) techniques and technologies. With the help of
image processing software, researchers and analysts have extracted substantial amounts of
data from satellite imagery. Data about vegetation coverage and condition can be derived
from imagery and mapped and integrated with other data using GIS. Another area where
GIS and satellite imagery has proved useful is in. In urban settings however, satellite
imagery has proved less advantageous. Until recently, the resolution of satellite imagery
available commercially was limited to 15 -30 meter pixel size. This meant that objects less
that 15 meters were not distinguishable. This grade of resolution often did not reveal the
details of the urban environment needed to study and track micro-scale information. So
although satellite imagery could produce broad urban land use classifications, much of the
information most valuable to urban managers and policy makers at a small, local scale was
not attainable. Recently, plans were announced for the commercial launch of satellites
capable of 1 meter and even sub-meter accuracy. This may prove to be a major step in the
utilization of satellite imagery in urban study. Aerial photography, another form of
remotely sensed data, has been a common method for gathering detailed urban land use
information.
This paper focuses on how GIS has been applied to establish, maintain and analyze urban
land use information to support the functions of local government in Logan, Utah. First,
the process of establishing baseline or historical land use information will be discussed.
Then the task of gathering and maintaining current land use is addressed. A brief analysis
of how land use has changed in Logan, Utah will be presented. And finally, how having
land use information stored in a GIS can help in the daily and long-term tasks of city
departments.
Region of Study
Logan, Utah is situated in the north central part of the state, approximately 90 north of
Salt Lake City. Logan lies in Cache Valley which is oriented north-south between the
Wellsville and Bear River Ranges of the Wasatch Mountains. The elevation of the city
ranges from 4500 feet above sea level in the west to 5000 feet along the foothills in the east.
Logan was settled in the early 1850's, shortly after the Mormon pioneers arrived in the
region. The town was established along the banks of the Logan River where water was
diverted to begin irrigation- based agriculture. Logan City was incorporated in 1866 and
became the primary center for commerce and cultural activity in Cache Valley. Today,
Logan is home to 38,793 residents. Enrollment at Utah State University numbered close to
20,000 in 1996. Over the past decade, Logan has experienced unprecedented growth. As of
1990, the population of Logan was 32,762 persons living in 11440 housing units (US
Census, 1990). In the 1995 Census revision, the population was 38,793 and there were
13,546 housing units (US Census, 1995). This represents a growth rate of nearly 4% per
year for the last 5 years. This growth has put tremendous strain on the city's
infrastructure and service capabilities. As Logan expands, land use changes and
intensifies. These changes effect every department in the city government. Land
development proposals need to be reviewed and approved by the Community Development
Department. Subdivision specifications and service requirements must be reviewed and
approved by the Public Works Department. As people move into the City, new utility
accounts are established for sewer and water connections and garbage collection services.
Methods
Establishing A Land Information System
The first step in this project was to create a land information database for Logan City. All of the land records for the City have been maintained by the Cache County Recorder's Office on tax assessor plat maps. Since the County does not operate a GIS, the property boundary maps were not available in a electronic format. This necessitated the creation of a digitally based property map for all the land within the Logan City limits. To accomplish this, the tax assessor plat maps were digitized into ArcInfo coverages. And existing subdivision information contained in the engineering software PALETTE, located in the Public Works Department at Logan City, were converted into ArcInfo coverages. As each coverage was digitized, the unique parcel number from the tax plat maps were assigned by using an AML. The AML was designed to speed the process of attributing. Since most of the plat maps were digitized one at a time, the book and page number (consisting of the first five-digits of the nine digit parcel number) were the same for the entire coverage. So by way of the AML, the user entered the book and page number for the coverage, and the AML allowed the user to place labelpoints in each polygon consecutively. This was a great help in shortening the often frustrating task of attributing.
When the entire areal extent of property in Logan had been digitized and attributed with
the unique parcel number, a complete parcel map of the city was created using the
MAPJOIN command in ArcInfo. This resulted in a City-wide representation of
property boundaries available both digitally and in hardcopy formats. This parcel
coverage is also the basis for the multipurpose land information system that Logan City is
developing.
Land Use Coding System
Logan has not maintained land use information in the past. Consequently, a system for designating land use needs to be established. Because of the similar conception and layout of the two cities, Logan's land use codes will be a modification of Salt Lake City's codes. Each is based on the grid pattern set forth by Mormon Leader Brigham Young. Each city also serves a similar functional purpose, though at different scales. The detail and specification of land use codes was determined by the Public Works and Community Development Departments in conjunction with the Information Services Department. A list of the more specific codes follows
In order to more easily view and perform analysis at a broader level, the detailed land use
codes were aggregated into a broader classification system which was a bit more intuitive
to the end user.
Acquiring Land Use Data for 1977
In order to determine urban land use change in Logan, land use data needed to be gathered
for a base year. Because there is no existing land use inventory, an alternative source for
land use data was needed. The Public Works Department has on file sets of aerial
photography for the year 1977. These aerial photos are at a 1:600 inch scale and cover the
entire city. At this resolution, features of the urban environment are easily distinguishable.
Using a hard copy of the property parcel map, land use codes were assigned to each piece
of property on the map by the visual interpretation of the aerial photography. The land
use codes from the map were used as the basis for populating the Land Information System
with 1977 land use codes. This resulted in a 1977 land use code for every piece of property
in the Land Information System.
Acquiring Current Land Use Data
In order to compare land use and thus obtain land use change data, a subsequent year's
land use data was needed. The City also had aerial photos at the same scale as the 1977
photos for the year 1989. It was determined that a more current inventory of land use
than 1989 was desirable for a couple of reasons. First, the 1989 data would not reflect the
changes from 1989 to the present, thus making the data 7 years outdated before it was even
gathered. Second, in order to establish a more accurate base for land use studies in the
future, a visual survey of current land use was deemed a more preferable and useful
alternative. Therefore, with a property map in hand, a manual survey of existing land use
was conducted in Logan. Land use codes were again entered for each piece of property on
the map. Then the land use codes from the maps were used to populate the Land
Information System with current land use codes. The result is a current land use code for
every piece of property in the Land Information System.
Developing a Methodology for Detecting Land Use Change
The main focus of this project was to determine whether or not GIS techniques can be an
effective tool in detecting and monitoring land use changes at a micro, urban level. This
was accomplished in the following way. A methodology for analyzing land use change in
the ArcInfo environment was created. In broad description, the steps include the
creation of a script in Arc Macro Language (AML) that automates the process of detecting
land use change based on the land use codes contained in the Land Information System. In
this AML the value of the current land use code is checked against the value of the 1977
land use code for each parcel. If the land use codes are equal, then no change has occurred
between the two years. If the land use codes are not equal to each other, then there has
been a change. If there has been a change, the AML will detect that and make a record of
the incident. When all the parcels have been searched, the AML produces two forms of
data. The first is a list of statistics on land use change. This list includes what 1977 land
use changed to what current land use by parcel. For example, if a parcel had a land use
code of agriculture in 1977 and its current land use was deemed single family residential,
the AML would produce a report with the area of the parcel, the 1977 land use code and
the current land use code. With this information, urban managers and decision makers
can quantify the extent of land use change as well as the type of land use change. The
second form of land use data produced is a map of land use change. This is created in a
similar process as the statistical report. But instead of producing a spreadsheet-type file, a
map will show which properties have undergone a change in use and the land use they have
changed to.
Description of Land Use Change in Logan, Utah
At press time, statistics of land use change and detailed maps of land use change by
category were not available for publication. The following images are inclusive of all land
use categories and cover the entire extent of the city. In general, Logan has seen a
depletion of open space and agricultural land to the development of housing and industrial
uses. This has occurred primarily in the western part of the city with the change to
industrial uses confined mostly to the northwest quadrant. This has been a function
primarily of zoning ordinances. To a certain degree, a substantial chunk of land has been
preserved as open space and wetlands with the creation of the Logan River Golf Course in
the southwest part of the city. Another major change has been the expansion of single
family units on Logan's eastern edge. Agricultural land has been developed into housing
units clear to the base of the mountains. Houses are even being built on land that once was
gravel pits in this area. The commercial land use in Logan has remained along the
traditional spine of Main Street. Its growth has expanded along Main Street both north
and south of the Central Business District. Multi-Family units have increased dramatically
in Logan in the past 20 years. Although the statistics will probably be slightly exaggerated
because it is hard to distinguish a house being used as a single family residence and a house
being used as a multi-family unit from aerial photographs, there has been a substantial
increase in multi-unit residences. The most dramatic increase is in the northwest part of
the city. Other areas of increased use are found around Utah State University and in the
southwest part of Logan. A noticeable absence of multi-family development is noted along
the eastern edge of the city.
Conclusion
Since 1992, Logan City has established and maintained a GIS. It is constantly in the process of growing and evolving. A major step in the development and usefulness of the GIS was the creation of a Land Information System. With the property boundaries now available in a digital format, and a link to other databases via the unique parcel number, Logan City is on the verge of exponentially expanding its GIS capabilities and departmental applications.
In terms of land use information, a cursory study of land use change between the years of
1977 and 1997 has been accomplished. Again, GIS has proved to be a useful instrument in
making land use and land use change data more accessible and useful to urban managers
and decision makers. Through its data structuring, analytical capacity and graphical
display, Esri products have been key in the development of GIS at the City of Logan,
Utah.
Author Info
Paul Morgan
Graduate Student
Utah State University
e-mail Sl369@cc.usu.edu
Helen Kenyon-Bares
GIS Administrator
City of Logan
e-mail Hbares@ci.logan.ut.us