Introduction to Earth Systems: Lesson 15 Maps and Other Images Reading Assignment: David Greenhood, Mapping, Chapters 1 and 2 NAVIGATION (To return, use back button) Reading Key Concepts Discussion More Links Exercises
Side Notes	Key Concepts	Links
Maps vs. photographic images	These are the key concepts in this lesson. You should be able to define or describe them after you have read this lesson, finished the assigned reading and explored the links. You should also be able to do the exercises and answer the questions at the end of the lesson. maps vs. photographic images digital elevation model (DEM) file format computer cartography uses of themes in decision-making Photographic Images In its simplest form, a photographic image is an attempt to duplicate human vision. Variations on that are obtainable with special filters and lenses. Until recently, all photography produced analog images, i.e. those obtained with traditional cameras that record images on film or plates. Recent development of digital cameras enables electronic storage of images for later transfer to a computer, where they are available for processing as digital images. Currently, the finest grain available in film is finer than the images obtainable with high-resolution digital cameras, but capability of digital cameras is increasing rapidly. Analog images can be transformed to digital data either through special development processes or through use of optical scanners. Maps generally are deliberately selective and, in that respect, are fundamentally different from photographic images. Of course, an extreme use of an aerial photograph could be as a map of everything visible. But the special usefulness of maps is in their selectivity, e.g. road maps, political maps, weather maps, etc. And since they are not intended to be photographic, they provide focus on special themes, e.g. highways and cities, to the exclusion of photographic detail. In place of detail that is not the subject of the map, the visual themes are usually accompanied by overlays of names and commentary that amplify the map symbols.	How GIS works -- from ESRI
Images are derived from data through a variety of methods.       Maps illustrate location in many contexts.	As described in Lesson 14, there are many digital file formats designed to make data storage and access more efficient and to address other special needs. The TIN format described in Lesson 14 is such a format. Another is Digital Elevation Module (DEM). DEM data, which records elevation of a portion of Earth's surface, is gathered with airborne sensors. Data is gathered in raster form and an elevation is associated with each point of the raster array. Image files are derived from the DEM data and computational methods are used to interpolate among the data points in order to illustrate the shape of Earth's terrain. DEM files are used to construct three-dimensional models of Earth's surface and two-dimensional renderings of it. Maps and GIS methods, i.e. the use of database themes and layers, are applicable in many contexts other than describing Earth's surface. Layered maps of interiors of buildings showing various types of infrastructure, room configuration, furniture, emergency escape routes, labels according to function, etc., are used for facilities management and maintenance, and other purposes. Maps of human anatomy, in which x-rays, magnetic resonance imaging and ultrasound imaging are used to make accurate images of size, shape, intersection, etc., are essential in many areas of medical diagnosis.	USGS Survey data; explanation of data formats
"Maps" for illustrating betweenness and intersection	Maps without measure In common use, maps display enough evidence to determine intersection and approximations for distance. With projections from non-planar surfaces to planar surfaces, e.g. from Earth's surface to a plane, not all of distance, shape and area can be preserved. Some distortion is inevitable. But there are usually clues, e.g. latitude and longitude lines/curves to enable the approximations. But while tolerance of such distortion is subjective, there is no such tolerance of errors in topology, i.e. intersection and betweenness. Intersections along a road cannot be shown in a wrong sequence; boundaries cannot appear to intersect if in fact they do not. Illustrations that are topologically correct but that compromise correctness of distance and area, e.g. to facilitate reading or to save space, are used in special contexts. For example, diagrams of public transportation systems, also called "maps", represent stops and intersections in their correct orders along routes and, in the interests of simplicity, tend to sacrifice shapes and visual accuracy of distances. Such single-purpose illustrations, while they are used as maps, are not likely subjects for GIS methods using digital file formats to manipulate themes and overlays.	Map of the London Underground
Custom construction and refinement of maps	Computer cartography As is the case with use of computers in many other applications, their use in the generation of maps introduces enormous flexibility, and it simultaneously forces precise organization and quantification of tasks heretofore handled easily by intuition or visual perception. The flexibility is discussed in Lessons 13 and 14. The ability to display layers representing subsets of the GIS database obligates the programmer to address some companion issues. Selection and placement of correct, attractive and useful labels vary with the composition of a theme, its purpose and its scale. For examples, sizes of type should be in keeping with the size of the image, variation in sizes of type should conform to magnitudes of the objects labeled, placement of labels with respect to their subjects should be consistent, and labels should not obliterate important landmarks. The credibility of visual non-textual forms, such as coastlines, political boundaries and contour curves, is subject to inter-relationships among density of data, computer screen size and screen resolution. Computational methods for augmenting sparse data are used at several levels. Where the data is not sufficient to support available screen resolution, e.g. in cases of sparse or outdated data, there are computational methods for supplying additional data, i.e. to interpolate using existing current data, to create plausible images. In cases of subjects under continual change, e.g. weather maps and ocean coastlines, there are methods for extrapolating on existing data, e.g. historical weather data, or on observations about self-similarity of coastlines.	Interactive selection of views of Earth         Interactive map maker: route maps
Use of themes to provide focus for decision-making	Data --> Information --> Decision-making Using GIS techniques, themes can be inferred from databases and can bring focus to visual reports. The databases are designed to facilitate collection and use of the data. Without organization and without context, data offers no intrinsic value. Subject to the quality of the data and to the database design, similarities and contrasts can be quantified and observed, thereby producing information, and can be illustrated interactively. The resulting maps and tables might produce justification for decisions and directions for action. For example, from comprehensive statistics about a given city, we can display separate maps showing household income distributed by location, preferences for political party in the last national election distributed by location, and ages of occupants distributed by location. These are themes displayed as foreground or on maps that do not display other data. "Location" here could mean city block, identified neighborhoods, boroughs, etc. We would now have visual displays of information derived from the data. Viewing the overlays of the themes, along with examination of supporting tables of data, might produce conjectures, about correlation among income, age and political preference. The conjectures, and perhaps verification through further sampling, might determine or support campaign strategies for the next election, In a different setting, i.e. a large farming operation, a database describing large plots of land could include data about various aspects of soil quality, crop history, tendencies toward erosion, etc. Analysis of various themes would quickly produce information in the form of interactive maps and tables. Overlays of the themes could then show compatibilities among soil composition, other relevant conditions and crop success. These observations enable the making of decisions about selection of crops for specific portions of land, time for planting, need for fertilizing, etc.	GIS data for California      Description of GIS project         Sample GIS project with instructions
	Links The Internet and GIS data GIS environmental examples in the Southwest USA Spatial data for California State and local GIS data Data availability in California Access to GIS data and geography-related Web sites.