| AIRBORNE/GIS: Monitoring Land Use Transformation
Land use in Salisbury, Md. is mapped with the combination of remote sensing data and GIS.
By X. Mara Chen The rapid growth of a community often brings about a mixed blessing. On one hand, it accelerates the growth of the local economy, attracts more businesses, and creates more higher paying job opportunities. On the other hand, it presents unprecedented challenges and problems, such as how to accommodate the growth: the changes and demands in housing, infrastructure, community services, and historic and environmental preservations.
While a successful strategy for managing a rapidly growing community lies in a sound planning, mapping the temporal changes provides essential information for the planning process. In particular, land use transformation presents a reliable indicator of regional growth and change. This article describes the use of remote sensing imagery and a geographic information system (GIS) to monitor the impact of growth on land use at Salisbury, Md. over the 16-year period from 1980 to 1995.
Salisbury is the largest city in the Eastern Shore of Md. In fact, it serves as a regional economic and cultural hub in the Delmarva Peninsula. It is the focus of development in Wicomico County. From the U.S. census data, the population of Salisbury city has increased 35 percent over the past two decades (1970-1990). Because of the rapid sprawl around the Salisbury city, Wicomico County has become one of the most rapidly growing counties in the Delmarva Peninsula. According to the findings of the Maryland Office of Planning, the built-up developments have increased 36 percent from 1973 to 1990. The alarmingly growing trend is that agricultural land and woodland have steadily declined, and the Eastern Shore rural way of life is changing. Needless to say, monitoring the land use transformation of Salisbury is vital to the Wicomico County's long-term planning for sustainable development. Land Use Mapping
The accurate and precise land use mapping can be done through field surveys, but it would be a time-consuming and expensive task. Instead, this study done through Salisbury State University used remote sensing data to map the land use of Salisbury. Considering land use transformation a reliable indicator of growth, the study focused on the land use changes over two periods: from 1980 to 1989, and from 1989 to 1995. Therefore, multi-temporal imagery data were used. The data included 1980 B&W aerial photos at scale 1:40,000; 1989 color infrared aerial photos at 1:40,000; and 1995 SPOT multispectral imagery (Figure 2). The 1980 photographs were available from image collection at the department, and they were taken in March 1980 by the Agriculture Stabilization and Conservation Service. The 1989 color IR photographs were taken in April 1989, and they were products of the National Aerial Photography Program (NAPP), USGS.
The aerial photos are ideal for any detailed land use mapping because of their characteristics of large scale and fine spatial resolution. However, 1995 photographs were not available for the study area. As a result, high resolution SPOT satellite imagery was used. The acquired imagery was taken in November 1995, and was available both in print at 1:200,000 and in digital format, which is readily enhanced and enlarged through digital image processing.
In the process of interpreting the photos and imagery, five major land use categories were used. They included agriculture land, built-up, woodland, wetland, and waters. The agriculture land included some patches of barren land within the built-up areas, which might not be used as agriculture fields. The built-up category did not further differentiate among areas of residential, industrial, commercial, and major highway networks.
As a result of the interpretation, three land use maps (1980, 1989, and 1995) were compiled. To track the temporal changes of the land use, these three maps were then geocoded into the computer system and registered with one another for GIS overlay analysis. Change Detection Using GIS
Analytical capability is the most distinct and powerful aspect of a GIS. It allows people to perform spatial overlay and associated attribute data manipulation in an analysis. This land transformation analysis was done by using ARC/INFO and ArcView software, which are products of ESRI Inc., in Redlands, Calif.
The objective of the analysis was to identify the impact of growth on the land use change in the study area. It is well known that the impact of growth on land has been of global concern, and it can be described in various ways. However, the most important concern in land transformation is that more and more land has been used for housing and agriculture without a balanced planning. The specific purpose in this study was to delineate how much agricultural land, woodland, and wetland was lost to the built-up sprawl of Salisbury, and how much woodland and wetland was then converted into farmland.
Two spatial overlays and associated attribute data manipulation were done to fulfill the stated objectives. From the analysis results, Figure 1 shows that, in the 1980 the agricultural land took 40 percent of the total land area, built-up area 26.7 percent, and woodland 28.9 percent. Clearly, it still depicted a typical Eastern Shore rural way of life: agriculture is dominant, and woodland was abundant. By the end of 1995, however, the land use patterns changed significantly. The built-up occupied 35 percent of the land area, and agriculture dropped to 33.8 percent, and woodland 26.8 percent. An overall land transformation trend over the 16 years was revealed: built-up areas have increased 31 percent, agriculture land, woodland, and wetland have decreased 15 percent, 7 percent, and 5 percent respectively. The analysis also presented a different land transformation trend for the 1990s as compared to the 1980s. From 1980 to 1989, Nearly half of the built-up expansion was at the expense of woodland and wetland. The built-up sprawl from 1989 to 1995, on the other hand, was largely at the cost of agriculture land, and thus the loss of woodland and wetland was much slower.
Furthermore, Figure 3 presents the spatial pictures of the land use change in the two periods. In the 1980s, the built-ups were largely concentrated within the metro core of Salisbury city, and the developments were along the waterfronts and around previously existing built-up areas. From 1989 to 1995, however, the built-up areas were dominantly outward sprawls, the developments were much larger in size and scattered in distribution, such as newly-developed large areas along east U.S. Route 50 and north U.S. Route 13. Overall, the growing trend was revealed as small-sized developments adding to the density of the previous built-up areas in the 1980s, and large-sized suburban sprawl in the 1990s. Summary
GIS and remote sensing hold a great potential in monitoring the growth of a community and assisting urban and regional planning. In this study, GIS quantitatively identified and delineated the impact of Salisbury growth on its land use transformation, and effectively mapped where the growth took place. The established land use database is in digital format, which could be readily used for future long-term monitoring of land use transformation, or for other environmental applications. Acknowledgments
This project was supported by the Office of Grants/Sponsored Research at Salisbury State University. The author would like to thank several students, J. Malinowski, C. Middleton, K. Pattison, and W. Short, for their assistance in geocoding the data. Helpful review of this paper by Dr. G. Welsh is gratefully acknowledged. About the Author:
X. Mara Chen is an assistant professor at the Department of Geography and Regional Planning, Salisbury State University, Maryland. She may be reached at 410-543-6460 or by e-mail: [email protected] Back |
