Las Vegas Urban Growth Date: 09/14/2014
Jenjira Holmes
Abstract As we all know, Las Vegas is one of the most urbanized cities in the United States. We do know for sure that Las Vegas is expanding in terms of the area, but we don’t know by how much. Therefore, I would like to investigate how much Las Vegas grew over the past 15 years. Satellite is a relatively new technology and therefore the data is also relatively new. It is best to investigate the recent time frame rather than going back more than 30 years with insufficient data. From the results, I found out that Las Vegas expanded dramatically from the end of the 20th century to the very beginning of the 21st century when the tourist industry boomed. From around the beginning of the 21st century, Las Vegas was still expanding, but not as fast as it used to be.
Index Terms Las Vegas, Urban Sprawl, Urban Change, Landsat TM5, Landsat 8, OLI, Change Detection Analysis, Classification, Unsupervised Classification, ROI, ENVI
This is one of the works done by U.S. Geological Survey in 1992 using Landsat 5. [Link: http://earthshots.usgs.gov/earthshots/Las-Vegas#ad-image-5]
Introduction The town of Las Vegas was established in 1905 by the auctioning of land. During the beginning of the 20th century, Las Vegas was just a stop along the railroad. The city then started to grow during 1930s, with the construction of Hoover Dam. Around 1940s, the gaming industry started to boomed and more hotels and casinos started were constructed. This also cause the population to grow rapidly. Las Vegas became a major convention center in the 80's and 90's because there were more entertainment attractions and amusement parks.
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Dolor Sit Amet There has been similar work that were done before about the urban sprawl of Las Vegas. One of this is done by the U.S. Geological Survey.
They did a dramatic illustration of the spatial patterns and rates of change resulting from urban growth. They observed the transportation data and how it had an effect on the population from 1907 to 1995. [Link:http://geochange.er.usgs.gov/sw/changes/anth ropogenic/population/las_vegas/]. The difference between my work and work that has been done before is probably the time span. The most recent work that others had done only cover until 2010 whereas my work covers the most recent changes in Las Vegas. Also, my work explore different land cover in Las Vegas and how much it evolves over time.
Data Description Study Area: The study area will be Las Vegas, Nevada. The coordinates of Las Vegas is 36.1215 N and 115.1739 W. It has the total area of 135.9 square miles or 352 square kilometer. Landsat Data: Since I would like to observe the change of Las Vegas over the past 15 years, I need to compare several images of Las Vegas This is the first image I used. This image is recorded during the day time on 1st of January, 1999. The satellite and sensor is Landsat TM 5. This image was recorded with the sun elevation: of 25.65574677 and sun azimuth of 152.32946015. The map projection level, datum and zone is UTM, WGS84 and UTM zone 11. This is the second image I used. This image is recorded during the day time on 24st of February, 2007. Same as the first image, the satellite and sensor is Landsat TM 5. This image was recorded with the sun elevation: of 38.59732725 and sun azimuth of 147.09217272. The map projection level, datum and zone is UTM, WGS84 and UTM zone 11. Lastly, this is the third image. This image is recorded during the day time on 22nd of August, 2014. Different from the first and the second image, the satellite and sensor is Landsat 8 OLI/TIRS. This image was recorded with the sun elevation: of 58.87938528 and sun azimuth of 135.76403306. The map projection level, datum and zone is UTM, WGS84 and UTM zone 11. I will only use Band 4,3,2 from all the acquired satellite images.
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Methodology Getting the Data: 1. To get the data to analysis, I went onto this website: http://landsatlook.usgs.gov/ 2. Choose location and date. Add to cart and check out. Extract the files and add band 4,3,2 into ENVI. ROI: 1. In the Basic Tools | Region of Interest | ROI Tool, select the Image radio button. 2. From the ROI_Type menu, select Rectangle. Draw a rectangle around Las Vegas. Right-click on the image to set the ROI. 3. From the File menu of the ROI Tool, select Save ROIs. Highlight the ROI and save this image to the Subsetting: 1. From the ENVI Main Menu, select Basic Tools | Subset Data via ROIs. In the dialog box, select the image and click OK. 2. In the next window, highlight the ROI in the Input ROIs window and save the new file into the local drive.
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Stacking: 1. In the Main ENVI toolbar Basic Tools | Layer Stacking. Import the three bands (4,3,2). 2. Make sure to order the files so that in the stacked image Band 4 becomes Band 1, Band 3 becomes Band 2 and Band 2 becomes Band 3. Use the option ‘Reorder Files’ to verify band order. 3. Save the result to the local drive. Unsupervised Classification: 1. Select Classification | Unsupervised | Isodata. 2. Select the stacked subset image in the following window and click OK. 3. Set the number of class to min – 4, max-10, the max number of iterations to 10, the change threshold to 5.00, the minimum number of pixels per class to 1000, the standard deviation to 1.00, the minimum number of merge pairs to 2. 4. Name the output file and save it in the local drive.
Results ROI Images and Statistics:
The red areas marked the boundaries at which Las Vegas expanded. The larger the red area, the larger the cities. The “Pixel Number” is the number of pixels represent the areas. The more pixels there are, the more, the larger the areas. Image 1 (year 1999): Pixel Number: 1,093,794 Image 2 (year 2007): Pixel Number: 1,507,736 Image 3 (year 2014): Pixel Number: 1,628,155 By looking at the pixel numbers of all the three images, we can be sure that the city of Las Vegas expanded over the last 15 years. The difference between pixel number in 1999 and 2007 is 413942 pixels whereas the difference in 2007 and 2014 is 120419 pixels. Therefore we can conclude that Las Vegas expanded faster from 1999 to 2007, and the rate became slower after year 2007 and onwards.
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Classification Images and Statistics: During the classification process, I have created 9 colored Bands. The colored Bands that represent the urban areas are two shades of green (Band 2 and 8) and three shades of purple (Band 6,7 and 9). By totaling up the pixels of all the 5 colored Bands, I will be able to calculate the pixel areas of Las Vegas.
Basic Stats
Min
Max
Mean
Stdev
Band 1
1
9
4.611595
2.156601
Histogram Band 1
DN 1 2 3 4 5 6 7 8 9
Npts 124814 419710 538853 483718 421476 329593 266817 248302 139280
Total 124814 544524 1083377 1567095 1988571 2318164 2584981 2833283 2972563
Percent 4.1989 14.1195 18.1276 16.2728 14.1789 11.0878 8.9760 8.3531 4.6855
Year 1999 Npts of Band 2+6+7+8+9= 1,403,702 pixels
Year 2007 Npts of Band 2+6+7+8+9= 1,301,085 pixels
Basic Stats Band 1
Min 1
Max 9
Mean 4.760312
Stdev 2.322077
Histogram Band 1
DN 1 2 3 4 5 6 7 8 9
Npts 123684 357080 463673 396271 337619 309173 236964 111292 286576
Total 123684 401572 945245 1341516 1679135 1988308 2225272 2336564 2623140
Percent 4.7151 13.6435 17.6763 15.1067 12.8708 11.7864 9.0336 4.2427 10.9249
Acc Pct 4.1989 18.3183 36.4459 52.7186 66.8975 77.9854 86.9614 95.3145 100.0000
Acc Pct 4.7151 10.3506 36.0349 51.1416 64.0124 75.7988 84.8324 89.0751 100.0000
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Basic Stats Band 1
Min 1
Max 9
Mean 4.723239
Stdev 2.313514
Histogram Band 1
DN 1 2 3 4 5 6 7 8 9
Npts 150098 319642 364885 390620 345056 304419 209780 80274 260894
Total 150098 469740 834625 1225245 1570301 1874720 2084500 2164774 2425668
Percent 6.1879 13.1775 15.0427 16.1036 14.2252 12.5499 8.6483 3.3094 10.7446
Year 2014 Npt of Band 2+6+7+8+9= 1,175,009 pixels
Acc Pct 6.1879 19.3654 34.4080 50.5117 64.7368 77.2868 85.9351 89.2444 100.0000
From calculating the pixel number of the classified Las Vegas, we can tell a lot about the expansion of Las Vegas. We expect the pixel number to larger as we progress from year 1999 to 2014. However, the classification told us that that numbers are actually getting smaller! This contradicts with our knowledge of the location. Therefore there must be mistakes during the process of classification. Some areas might not be classified correctly according to the land use of Las Vegas. Conclusion:
Population of Las Vegas
Since the classification of the images are not correctly defines, I will rely mainly on the data that I had created using ROIâ&#x20AC;Ś. Image 1 (year 1999): Pixel Number: 1,093,794 Image 2 (year 2007): Pixel Number: 1,507,736 Image 3 (year 2014): Pixel Number: 1,628,155 From 1999 to 2007 (8-year period), Las Vegas had expanded by 37.87 %. From 2007 to 2014 (7-year period), Las Vegas had expanded only by 7.99 %. Overall from 1999 to 2014, Las Vegas has expanded by 48.85%. It is said that Las Vegas is the fastest growing metropolitan in the country! Citations: "Urban Land Use Change in the Las Vegas Valley." Urban Land Use Change in the Las Vegas Valley. U.S. Department of the Interior U.S. Geological Survey, 5 Aug. 2013. Web. 10 Sept. 2014. <http://geochange.er.usgs.gov/sw/changes/anthropogenic/population/las_vegas/>. "Las Vegas, Nevada, USA | Earthshots: Satellite Images of Environmental Change." Las Vegas, Nevada, USA | Earthshots: Satellite Images of Environmental Change. U.S. Department of the Interior U.S. Geological Survey, 14 Sept. 2014. Web. 14 Sept. 2014. <http://earthshots.usgs.gov/earthshots/Las-Vegas#tabs-0>.