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------Using GIS-- Introduction to GIS NR 143 Study Overview: part 2 By Austin Troy University of Vermont
Introduction to GIS Map Projections • What is the shape of the earth? • What is a spheroid? • What is the geographic graticule/grid? How does it reference points on the earth? What’s the difference between medians and parallels? How does this relate to latitude and longitude?
Introduction to GIS Map Projections • What are the different types of distortion that can happen to a map? Shape, area, distance, direction. • Conformal maps preserve shape • Equal area maps preserve area • Equidistant maps preserve distance • Azimuthal preserves direction • Which are mutually exclusive? • Which are global versus local?
Introduction to GIS Map Projections • Complications • Satellites can be off slightly in positioning—this is called ephemeris. That error information is recorded and sent to the GPS units. • Atmospheric attenuation of signal—goes slower than speed of light in some parts of atmosphere—can be dealt with through predictive models
Introduction to GIS Map Projections • What’s the difference between cylindrical, conic and azimuthal projections? • What are some specific projections within those projection families? What properties are preserved by the major projections? • What’s the difference between Mercator and Transverse Mercator?
Introduction to GIS Map Projections • For each type of projection, where is the error least and greatest and why? What does the scale factor tell you about projection error? • Which projections are best for polar latitudes? Mid latitudes? Areas with east west orientation? North south orientation? Why is this and how does it relate to the way the projection surface touches the earth? • What are central meridians and the standard meridians in a projection?
Introduction to GIS Datums • What are they? Roughly approximates surface of earth at some mean sea level • What’s the difference between a surface based and spheroid based datum? • How do datums relate to spheroids? Translator of where spheroid meets actual locations on earth. • What is the relationship between datums and surface reference points? • Why must we give the datum when we give lat/long coordinates?
Introduction to GIS Datums • Why must we give the datum when we give lat/long coordinates? • What was the most common surface based datums? NAD 27. Which spheroid is it based on? Clarke 1866. • What’s the newer spheroid based datum: GRS80/NAD83/WGS84. • What is datum shift?
Introduction to GIS Coordinate Systems • What’s the difference between coordinate systems and plain map projections and when do we use one over the other? • Why are coordinate systems better for mapping larger-scale, more local level phenomena? • What is the difference between UTM and State Plane? For what purposes is one better than the other? • What datums are used for each?
Introduction to GIS Coordinate Systems • What projection is used in UTM? What are some common projections used in State Plane? • What’s the difference in required accuracies for UTM and State Plane? Why are they different?
Introduction to GIS GPS • How does GPS work? • Main components: • Satellites know where they are—they are reference points • GPS unit measures distance to at least four satellites based on the speed of light, then it can triangulate its position. • Can triangulate position because of the concept of intersecting spheres
Introduction to GIS GPS • Complications • How does it know when signal left satellite? Uses pseudo random to compare lags. In theory the code strings started at exactly the same time. • One on satellite is near perfect but not the ground receiver. How does it figure out error in ground time keeping? Uses fourth satellite signal to error check the clock. • How do we know where a satellite is? GPS unit keeps a digital almanac of their locations.
Introduction to GIS GPS • Complications • Satellites can be off slightly in positioning—this is called ephemeris. That error information is recorded and sent to the GPS units. • Atmospheric attenuation of signal—goes slower than speed of light in some parts of atmosphere—can be dealt with through predictive models
Introduction to GIS GPS • Selective availability • Old system of jamming signals to increase error, no longer used • Differential correction • Way of increasing positional accuracy by using moving and stationary receivers together. The stationary receiver “knows” where it is and error are compared. Formerly used for getting around SA but still used to increase accuracy.
Introduction to GIS Geocoding • What’s address geocoding? Uses address matching to place records on a street segment? Interpolates position on the street segment. • What is the output? Point layer • What kind of reference layer is needed? Streets layer • What attributes must it have? To and from address ranges and street names • What is a geocoding service in ArcGIS? • What is a geocoding style?
Introduction to GIS Geocoding • What are some the potential errors from address geocoding? Where can errors come from? • What’s the problem with geocoding in very rural areas? Why could there be more interpolation error? • How is xy geocoding different?
Introduction to GIS Scanning • Flatbed • Drum • Continuous feed • What is the scan output? Raster layer. • What can be done with it to create vector features? • Tracing, line thinning, line extraction, topological reconstruction.
Introduction to GIS Digitizing • Head’s up versus tablet digitizing • What is arc snapping and how does snap tolerance control it? • What are control points?
Introduction to GIS USGS Public Data:DLG • What scales does it come in? • What are some thematic layers available at different scales? At which scale is the most layer available from and at which scale the least? • What is a data dictionary and why is that necessary for using DLGs? • How can we determine if the layer we want is available at the scale we want?
Introduction to GIS USGS Public Data • What is the difference between NEDs and DEMs? What makes NEDs better and easier to use? • What is the difference between a DOQ and a traditional air photo? • What type of data shows all the named points from the USGS paper topo maps? • Other USGS data types: DRG, NLCD • What is the new transfer standard that is being used SDTS—spatial data transfer standard
Introduction to GIS TIGER Data • What features does this include? • What data is it derived from? • What’s so important about the TIGER streets data? • What is a FIPS code and how does that allow us to utilize census data? • What is the hierarchy of census units: state>>county>>tract>>block group>>block
Introduction to GIS Remote Sensing Principles • What is solar irradiance and electromagnetic radiation? • What’s the connection between electromagnetic radiation and electromagnetic spectrum? • What are the parts of the spectrum we use in RS? • Why is it important to be able to perceive in more than just the visible spectrum for telling things apart? • What is a spectral response curve and how does that tell us what spectral bands we’ll need for identifying objects with remote sensing?
Introduction to GIS Remote Sensing Principles What are some objects that you would expect would have very different spectral response curves and why?
Introduction to GIS Remote Sensing Principles • What is the difference between multi-spectral and panchromatic remote sensing data? • How are color composites made from multispectral remote sensing data? • What’s the difference between false and true color composites? • What is the difference between spatial, radiometric and temporal resolution?
Introduction to GIS Remote Sensing Satellites • What’s the difference between push broom and whisk broom scanners? Which types corresponds with along track and across track? What do SPOT, LANDSAT and IKONOS use? • What is the orbit type of those three satellites? What’s the importance of that type of orbit? • What’s the difference in spatial resolution between the three satellites? • Which has the most bands?
Introduction to GIS Remote Sensing Image Processing • What’s the difference between geometric and radiometric correction? • What are some sources of distortion requiring geometric correction and radiometric correction? • What’s the difference between point and local image enhancement operations? • Image enhancement: how are contrast enhancement and spatial feature enhancement different? Convolution: low pass and high pass filters.
Introduction to GIS Remote Sensing Image Classification • What’s spectral versus spatial pattern recognition? Which approach does object oriented classification use? • How are supervised and unsupervised classification different? When is one better than the other? What info is needed to do each? • How does object oriented classification work? What is feature extraction and how does it change at different levels of segmentation? What inputs are used? • What are advantages of object oriented approach?
Introduction to GIS Remote Sensing Image Classification • What is the Anderson system of classification? • What is the difference between Anderson levels 1, 2, 3 and 4? What are the data requirements for mapping at higher level? What levels do USGS use? • What’s an accuracy assessment and why is it so important? What’s the difference between user’s accuracy and producer’s accuracy? UA: % pixels classified as A that really are A. PA: % pixels classified as anything but A that really are A.
Introduction to GIS Data quality • Difference between accuracy vs. precision? How do they relate to cost? What are some applications requiring high precision? • What is positional accuracy? What is a measure of positional accuracy? • Attribute precision and accuracy: what’s the difference between precision in numeric and categorical attributes? • How does conceptual accuracy and precision relate to image classification?
Introduction to GIS Data quality: other measures • How are completeness and currency related? • How are logical consistency and topology linked? • How is conflation used to improve a layer? What are some possible examples? • What’s the difference between feature and attribute conflation? Which uses rubber sheeting?
Introduction to GIS Sources of error • How are systematic and random error different? How do random and systematic error relate to accuracy and precision? • What are some sources of error? Which might be systematic versus random? How might you introduce error into interpolations? What are some sources of classification error? What are some topological errors? • What are error propagation and cascading?
Introduction to GIS Metadata • What are some of the most critical facts to include in metadata and why? • What is the main US standard for metadata? • What are some of the most important metadata headings or categories to be included? • What types of data quality issues should the metadata address?
Introduction to GIS Terrain modeling • What are the different models for viewing terrain? DEM grids, vector contours, TINs. • What is the advantage of TINs over other types of terrain models? • How does the maximum z tolerance method choose how many and which sample points to use in making TIN triangles. • What is the method used to connect the sample points to make the triangles?