These images show the rapid growth of Las Vegas, Nevada. The tip of Lake Mead is visible east of the city, where Hoover Dam impounds the Colorado River. This is by far the fastest-growing metropolis in the United States. The population has grown in recent decades as follows:¹

       1964:   127,000
       1972:   273,000
       1986:   608,000
       1992:   863,000
       1997: 1,124,000

These are the same kind of standard false-color images that appear throughout Earthshots, simulating color-infrared aerial photographs. Remember "RGB = NRG": red, green, and blue in the image represent how much near-infrared, red, and green solar energy the ground reflects.

As the city expands you can see a sort of landcover succession through human construction. For examples, look at the 1992 zoom-in on the western suburbs:

Pre-construction land appears medium gray-green (medium gray-green) in the Landsat image. This color comes from sparse desert vegetation, reddish soils, and stone darkened by an inorganic patina of oxidization. (Point to a camera for a description, and then click on it to see the ground photo. Click an image to zoom out.)

Construction land appears brighter (brighter). Bulldozed soil, bare of vegetation, is very reflective.

A young neighborhood appears medium green (medium green) again, perhaps a bit brighter from all the reflective pavement and roofs. The trees are small, and some developments now conserve water by landscaping with rock and desert plants rather than grass.

An old neighborhood appears dark, brownish red (dark, brownish red), from the mature trees and more grass. In these false-color images, photosynthesizing vegetation always adds a red tint.

Golf courses appear bright red (bright red) because they are the most intense vegetation. New courses tend to be mixed into residential developments while older courses tend to be separate.

Water appears almost black (almost black) because at this angle it scatters little light back to the Landsat sensor. Like golf courses, water is sometimes integrated into residential developments for recreational purposes.

The change-detection image shown here summarizes many of the 1986-1992 changes in one image. It shows both changes in brightness (how reflective the land is) and greenness (how much healthy vegetation there is). To make this image, a computer:

• overlaid the 1986 and 1992 digital images precisely;
• calculated change-in-brightness and change-in-greenness for each pixel (greenness was calculated from the difference between MSS bands 4 and 2, since healthy plants reflect infrared energy strongly but visible light weakly);
• assigned a color to each pixel, according to where it lay on the greenness/brightness graph shown in the image (for example, a pixel that had become greener and brighter would be yellow); and finally,
• colored minor changes gray, leaving only the significant changes.

The landuse/landcover maps

Much of the same information is shown more simply and abstractly in the landuse/landcover maps shown here. These maps were made by interpreting aerial photographs. Basically, a landcover map shows objects (e.g. rock/gravel/sand) while a landuse map shows actions (e.g. extraction). There is often high correlation between the two; for example, most "recreation and memorial" (golf and cemetery) land is grass. The 1994 maps show landuse and landcover separately, but the 1973 classification is a combination of the two.

Even at this abstract, aggregated level, several natural and manmade structures appear. Highways pass through the city, and the airport stands out to the south. The Strip is visible in the center, and Las Vegas Wash curves away to the east. This wash hints at the incongruity between the two datasets, coded as "nonforested wetland" for 1973 and as "trees" for 1994.

Question

Between 1986 and 1992 a lake appeared along Las Vegas Wash. From the satellite images, can you tell how this reservoir is being used? (See the answer below.)

Big wallpaper

View a large version of the 1992 Landsat image, which you can set as your desktop wallpaper. It is 800 by 600 pixels, or about three times the area of the image to the left.

Footnotes

1. World almanac and book of facts, 1997, p. 385. From 1990 to 1994 the Las Vegas Metropolitan Statistical Area increased 26.2%; among areas over 600,000, Austin was second at 13.9%. The list of figures is from the Nevada Historical Society, and includes Las Vegas, Henderson, and North Las Vegas.

Other references

The Urban Retrospectives Research Program contributed the following document to the Internet workshop, "Impact of Climate Change and Land Use in the Southwestern United States": William Acevedo and others, 1997, "Urban Land Use Change in the Las Vegas Valley" [computer files]. Available as of 28 April 1998 at geochange.er.usgs.gov/ sw/changes/anthropogenic/ population/las_vegas.

Satellite images

DS1010-1047DF008 (Corona medium-resolution satellite photograph, 17 September 1964)

The 1972, 1986 and 1994 scenes are from the NALC dataset.

LM1042035007225790 (Landsat 1 MSS, 13 September 1972)

LM5039035008625390 (Landsat 5 MSS, 10 September 1986)

LM5039035009225490 (Landsat 5 MSS, 10 September 1992)

U.S. Geological Survey, 1997, Southwest U.S. change detection images from the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS); Las Vegas, Nevada: Sioux Falls, South Dakota, USGS EROS. (For more change-detection images, see "Southwest U.S. Change Detection Images from the EROS Data Center")

Maps

U.S. Geological Survey, 1969 (1954, revised 1969), Las Vegas, Nevada; Arizona; California: series V502, edition 5, scale 1:250,000.

U.S. Geological Survey, 1994 (1973 data), Las Vegas, Nevada, Arizona, California 1:250,000 Quad Land Use Map: Sioux Falls, South Dakota, USGS EROS, USGS Land Use and Land Cover (LULC) Data, scale 1:250,000. Data and metadata available through EarthExplorer and GloVis. These data came from the LUDA (Land Use Data Analysis) project, using the GIRAS system and data format.

U.S. Geological Survey, 1996, High resolution land use / land cover data for the Las Vegas, Nevada urban area, 1994: Sioux Falls, South Dakota, USGS EROS. This dataset was made by the USGS National Mapping Division for the USGS National Water Quality Assessment Program. Contact: USGS NAWQA.

Photographs

All photographs were taken on 17 March 1998 by Robb Campbell and Peter Devincentis, USGS. Photographs were taken at Golfside Drive north of Del Webb Boulevard, Lake Sarah from Breakwater Drive, Lake Mead Boulevard west of Del Webb Boulevard, and Vegas Drive across from Valley Drive. The Las Vegas Wash was photographed at the Rochelle Avenue service road. The main channel is not shown. The pre-construction vegetation was shot from along the gravel planned Beltway. The baseball field was shot from the top of the jungle gym slide.

This is Lake Las Vegas, a privately-owned lake which is part of a commercial residential resort. You can see that unlike Lake Mead, it is fringed with land which has been cleared for building. This appears as a bright halo in the 1992 Landsat image, and even more obviously as an orange halo in the 1986-1992 change image.