Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
A-1 One of the most useful sources of contemporary aerial pho- tography and topographic maps is the Microsoft TerraServer Web site (http://terraserver.homeadvisor.msn.com/). Figure A.1 shows the homepage of the TerraServer Web site. Infor- mation about navigating the Web site is available under the âAboutâ tab, but the basic steps to downloading imagery from this site are provided here. There are several ways of locating imagery at the Terra- Server Web site. The primary method is to type the name of a town or geographic feature near the area of interest in the box labeled âSearch TerraServerâ shown in Figure A.1. One can also left-click the mouse pointer on a spot on one of the green areas of the world map. If the geographic coordi- nates of a specific site are known, the user can left-click on the âAdvanced Findâ tab, which will send the user to the âAdvanced Findâ page shown in Figure A.2a. The user can search for a specific address, place, or stream gauge, or the user can search using geographic coordinates, as shown in Figure A.2b. When the user types in the name of the place of interest, a page may appear that has multiple listings with the same name from which the user can choose (see Figure A.3). This âFind Resultsâ page lists available aerial photography and topographic maps for the various sites with the same place name. Once the user has chosen a particular location, left- clicking the mouse button on the image of choice brings up the image page. Figure A.4 shows the image page with a portion of a topographic map for an area near Judson, Min- nesota, and Figure A.5 shows the page with an aerial photo- graph for the same area. The toolbar at the top of the map or photo image page contains several tabs that allow the user to adjust the size of the image viewed, to zoom the image, to view the scale and coordinate details of the image, and to download the image. A zoom bar allows the user to zoom the image, and the arrows around the image are used to move the image laterally. The types of topographic map images shown are depen- dent on the resolution chosen. For example, map images with resolutions of 4 m or greater are from 7.5-minute series topo- graphic quadrangle maps (scale 1:24,000). Map images with resolutions between 16 m and 4 m are 15-minute topographic quadrangle maps (scale 1:62,500), and images with map res- olutions less than 16 m are 1 degree à 2 degree topographic maps (scale 1:250,000). TerraServer images of aerial pho- tographs are also based on the image resolution chosen. Each image of a map or aerial photograph has a resolution based on the number of pixels that make up the image. For example, the images shown in Figures A.4 and A.5 have res- olutions of 16 m, meaning that each image pixel covers 16 m. To determine the number of pixels in each image, as well as the coordinates of the image, the user selects the âInfoâ tab at the top of screen as shown in Figures A.4 and A.5. The âImage Infoâ page (see Figure A.6) provides the image size in pixels, the size of each pixel, the coordinates of the image, the date the image was photographed, and the Universal Transverse Mercator Zone on which the image is projected. The images can be downloaded and saved in JPEG format. In addition, World Files containing the image coordinates and other information in ASCII format can be downloaded or printed out for use with GIS applications. The âDown- loadâ tab at the top of the screen (as shown in Figures A.4 and A.5) is selected for downloading the image shown. The image can be downloaded free of charge (see Figure A.7). The number of images that will need to be downloaded is dependent on the resolution required and the area of cover- age. The more the image is zoomed in, the greater the reso- lution and the greater the amount of visible detail. However, the user will need to download and splice together a greater number of the high-resolution images to cover a specified area. This is easily done using the World Files in GIS and CAD software, but it can also be done easily using most graphics-editing software. APPENDIX A DOWNLOADING MICROSOFT TERRASERVER IMAGES FROM THE INTERNET
A-2 Figure A.1. Home page for Microsoftâs TerraServer Web site.
A-3 Figure A.2. Two TerraServer pages: (a) the âAdvanced Findâ page, which allows for searches to be conducted using addresses, place names, stream gauges, and geographic coordinates and (b) the âGeographic Coordinate Searchâ page. (a) (b)
A-4 Figure A.3. TerraServer âFind Resultsâ page with multiple map and aerial photo listings for sites with the same place name (Judson).
A-5 Figure A.4. TerraServer topographic map page for Judson, Minnesota.
A-6 Figure A.5. TerraServer aerial photograph page for Judson, Minnesota.
A-7 Figure A.6. TerraServer âImage Infoâ page with detailed information about the aerial photograph taken of an area near Judson, Minnesota.
A-8 Figure A.7. TerraServer âDownloading USGS Aerial Imageâ page for an area near Judson, Minnesota.