ArcNews Online

Spring 2002
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Imagery Fuels Enterprisewide GIS

Viva Las Vegas!

Las Vegas, Nevada, home to more than 1.5 million people, is the entertainment destination of32 million people each year. Apart from the bright lights, stage shows, casinos, and other man-made excitement of this "diamond of the desert" is the Las Vegas Wash, an area of unexpected natural beauty and lush vegetation that attracts both desert inhabitants and water-loving creatures alike. As far back as 1,000 years ago, the Las Vegas Wash supported a variety of Native Americans, Spanish explorers, farmers, and miners with its abundant natural resources.

In recent years, maintaining the delicate balance between the needs of a growing population with those of plant and animal life in the wash has rallied many valley residents and become the cornerstone of an enterprisewide GIS that relies on imagery for current, accurate, and highly visual information.

About the Wash

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IMAGINE OrthoBASE is used to register the aerial photos collected every six to eight weeks by the Las Vegas Wash Coordination Committee. Once rectified shapefiles are updated, using IMAGINE Vector module, by digitizing the interface between the delta and Lake Mead. Shapes are then attributed with date and lake elevation.

Occupying a 12-mile stretch of land in the southeast portion of the Las Vegas Valley, the wash averages 153 million gallons of daily water flow and is the primary drainage channel for all stormwater, urban runoff, shallow groundwater, and highly treated effluent. Wetlands serve as a polishing mechanism as flows move through the wash, under Lake Las Vegas, and to Lake Mead and the Colorado River system. Lake Mead, the largest man-made reservoir by volume and a designated U.S. national monument, provides approximately 85 percent of the water supply for valley residents and some 12 million people living in Arizona and California.

The wash supports diverse plant and animal species and at one time contained about 2,000 acres of wetlands. In the past 30 years, that number has diminished to 300, a byproduct of increased flows in the wash resulting from rapid population growth.

Fortunately, Leica Geosystems' ERDAS IMAGINE software and Esri's GIS software have provided an enterprisewide solution that serves many private citizens; Businesses; universities; and local, state, and federal agencies cooperating to protect and manage the wash.

Citizens, Agencies Unite

In 1997, complex issues and growing concerns over water quality in the wash and Lake Mead led the Nevada Division of Environmental Protection (NDEP) to form the Lake Mead Water Quality Forum, joining local, state, and federal agencies interested in environmental, water quality, and research concerns. Within months, the Southern Nevada Water Authority (SNWA) formed the Water Quality Citizens Advisory Committee (WQCAC) to prioritize issues/actions related to protecting the water quality of the area. Soon, WQCAC recommended the formation of the Las Vegas Wash Coordination Committee (LVWCC) (see Imagery Is a Valuable Data Collection Tool), a stakeholder group organized by SNWA that unites 28 agencies from cities, counties, academic institutions, private corporations, federal agencies, and nongovernmental organizations (NGOs).

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For each aerial photo captured by the Las Vegas Wash Coordination Committee, three to four ground control points are collected in order to register the image to the State Plane coordinate system. Once registered, the images are documented and indexed and ultimately used in time series analyses to document the changes occurring through the Wash.

LVWCC's GIS/remote sensing staff forms the epicenter of all wash activities. The staff manages and coordinates all types of data, initially centralized in ArcInfo and now in ArcGIS 8.1, to support various study teams as they identify issues and develop specific recommendations for the wash. The database is routinely updated with aerial photos processed with ERDAS IMAGINE software, and Web sites are maintained to facilitate access and data sharing between study team members, other agencies, and the public.

According to Kim Zikmund, LVWCC's project manager, the committee's framework "allowed people to consider all of the issues at the same time." The first recommendations were rolled into a comprehensive plan made available online ( "We have very aggressive plans to enhance and stabilize the wash," says Zikmund. "The comprehensive plan provides specific, on-the-ground recommendations that we can act upon, thereby providing for the long-term management of the wash."

Every GIS Has Its Story

GIS in Las Vegas Valley dates back to 1982 when the Clark County Planning Department started a land use inventory program using ArcInfo, followed by a parcel conversion program in 1989 that launched an interlocal agreement to share and support GIS development. Parcel and water facilities were converted using digital orthophotography, the valley's first use of remote sensing for data collection. Later, in 1991, the Las Vegas Valley Water District used ERDAS IMAGINE to analyze Landsat Thematic Mapper imagery and develop vegetation classification maps for 60 hydrographic basins for water rights applications in other Nevada counties.

"As our capabilities have grown, our use of GIS and remote sensing has grown too," says Art Ehrenberg, LVWCC's GIS/advanced research analyst. "We now have 13 local government agencies that support, contribute, and maintain data and 12 other agencies and private organizations that access the data by subscription. All are sharing data in the Clark County GIS repository." To date, 77 projects in 15 categories ranging from archaeology, biological studies, education, and erosion control to flow gauging, photography, recreation, sediment sampling, water quality, and wetlands have been documented.

Imagery Adds New Data Quickly

Aerial photos dating back to the 1930s, site photos, and project information have been indexed and registered, helping the LVWCC GIS team document temporal changes in the wash. Adding one-foot resolution digital aerial photos collected by Clark County since 1998, supplemented by low altitude high-resolution aerials LVWCC collects every six to eight weeks, helped establish baseline data coverages for monitoring progress and impacts along the wash.

"This area is undergoing rapid change," explains Ehrenberg. "Aerial photos are a great method of adding data quickly to your GIS and augmenting work in the field. We now have access to current, very detailed imagery on a regular basis." The low-resolution aerial photos are scanned at 1,000 dots per inch (dpi), yielding 3/10-pixel resolution, and at 96 dpi for thumbnails used to index each aerial photo and register it to a basemap.

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Location map shows the spatial relationships between the Las Vegas Valley and the Las Vegas Wash.

New GIS and geographic imaging tools are added to match the study team's requirements and, according to Ehrenberg, they now "use just about every Esri and ERDAS product available." Currently, IMAGINE OrthoBASE is used for mosaicking and orthorectification. By mid-2002, LVWCC will upgrade to the full ERDAS Photogrammetry Suite for additional 3D GIS capabilities via elevation and 3D feature extraction tools.

Helping nontechnical people grasp the issues facing the wash is a priority for LVWCC. "Three-dimensional visualization helps us explain projects and communicate the current conditions of the area," says Zikmund. "Imagery and GIS help people understand in tangible numbers what they are seeing, which helps us all better manage our resources."

"Three-dimensional visualization is an important tool when presenting data," explains Ehrenberg. "We create 3D fly-throughs with IMAGINE VirtualGIS for showing areas of the wash. Many people don't immediately understand 2D, but in 3D the results are more dramatic and the visual impact really aids in the understanding of a problem or result."

A Portable and Interactive Future

ArcGIS 8.1 and IMAGINE Professional 8.5, along with their extensions and add-on modules, are the backbone of the GIS and the main tools for acquiring, updating, and analyzing the data. ArcView 3.2a supports many of the hydrologists, biologists, and other professional field staff and researchers with basic mapping and image analysis needs. By mid-2002, LVWCC expects to integrate ArcIMS into the existing Web sites, making maps more current and interactive, and ArcPad technology into fieldwork, making the GIS more portable. "If people can query the data in the field, it not only helps them, it also helps us by streamlining data input," says Ehrenberg. "This will save us a lot of time and greatly reduce errors in the system."

Establishing data standards is a challenge because of the various data entering the system. As data integration has become easier, evolution in software design and import capabilities also make it easier to incorporate any type of data (including CAD) much faster. "Standards will help completely automate the process, decrease errors, and increase data availability," says Ehrenberg.

Currently running on UNIX and Windows NT systems, most of the GIS data is, or will be, stored in ArcSDE coverages linked with the databases warehoused in Oracle 8.1. Since most data is queried or accessed by member agencies or the public through the Web, development of Web-based solutions is the thrust of future development initiatives.

"Accessing real-time imagery and data on the Web will enable the community at large to visualize geographic information 24 hours a day, seven days a week," says Zikmund.

For more information about the Las Vegas Wash, contact Art Ehrenberg (tel.: 702-822-3383, e-mail:, Web: For more information about ERDAS IMAGINE, contact Leica Geosystems (tel.: 877-463-7327, Web:

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