GIS 1 - Midterm

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akatherine
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284743
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GIS 1 - Midterm
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2014-12-11 00:45:48
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GIS terms for exams
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  1. Coverage
    • the oldest vector format, developed for Arc/Info.
    • contain multiple feature classes, which may store points, arcs, polygons, and polygon labels.
    • also store topology, and the tables have several attribute fields reserved for this purpose.
    • Do not use Windows to copy or delete coverages, shapefiles, and geodatabases. Always use ArcCatalog to delete or copy spatial data sets.
  2. Aspatial data
    Data that is not or only incidentally tied to a point on the Earth’s surface
  3. Nodes
    endpoints of the line
  4. vertex
    intermediate points between nodes
  5. polygon
    a group of vertices that define a closed area
  6. feature class
    • features grouped together into data sets
    • only 1 kind of geometry per data set
    • can include point features, line features, or polygon features but never a combination
  7. attributes
    • information stored about them, such as their names or populations
    • This information is stored in a table
  8. Feature ID (FlD) or ObjectlD (OID)
    links the spatial data with the attributes
  9. thematic mapping
    one example of how linked attributes can be used to analyze geographic information
  10. feature datasets
    made up of multiple data classes all being related to each other in some way
  11. spaghetti model
    stores features of the file as independent objects, unrelated to each other
  12. examples of topological features
    • adjacency
    • connectivity
    • intersection
    • overlap
  13. Logical consistency
    evaluates whether a data model or data set accurately represents the real-world relationships between features
  14. large scale map
    • a map in which the outcome will be large and the denominator is small
    • Ex: a campus map is larger scale than a city map
  15. Thematic accuracy
    Accuracy of attributes associated with the map
  16. Spatial resolution
    At what distance interval measurements are taken or recorded. What is the size of a single pixel of satellite data?
  17. Temporal resolution
    How frequently measurements are taken
  18. Precision
    number of significant digits used to record a measurement or the statistical variation of a repeated single measurement
  19. Steps for planning a drawing
    • Determine the objectives of the map
    • Decide on the data layers to be included.
    • Plan the layout
    • Choose colors and symbols.
    • Create the map
  20. Four properties of map features may be distorted by projections:
    • area
    • direction
    • distance
    • shape
  21. Datum
    a combination of an earth ellipsoid and a reference point to reduce mapping discrepancies
  22. Map extent
    the range of x-y values currently displayed in the data frame. Zooming in reduces the map extent; zooming out enlarges it.
  23. 3 Ways to scale
    • Automatic: image adjusts based on data frame
    • Fixed scale: defined scale
    • Fixed content: adjusts the scale but locks in the extent of the map
  24. 3 types of databases
    • Flat file
    • Hierarchical: multiple files with fixed relationships
    • Relational: multiple files with flexible relationships
  25. SQL
    Structured Query Language
  26. key field
    The tables are combined using a common field called a key. The key field must be of the same data type in both tables.
  27. cardinality of a relationship
    • Dictates whether the tables can be joined.
    • The Rule of Joining stipulates that there must be one and only one record in the source table for each record in the destination table.
    • The destination table is the point of reference and comes first; that is, the relationship cardinality is reported as {destination} to {source}.
  28. a geographic coordinate system, or GCS
    Latitude and longitude system
  29. 3 types of map projections
    • Azimuthal (flat)
    • Cylindrical
    • Conic
  30. UTM
    • Universal Transversal Mercator
    • a secant transverse cylindrical projection
    • distortion is negligible within a single zone
    • convenient because users need only know the zone number and hemisphere
    • has 60 north-south zones, each 6 degrees wide
    • World wide used
    • Unit: meters
    • UTM Zones: e.g. 14N
  31. State Plane Coordinate System (SPCS)
    • Includes an assortment of coordinate systems developed in the 1930s
    • distortion is negligible within a single zone
    • uses all 3 projections, depending on the zone and its orientation
  32. spatial reference includes
    • Coordinate system
    • X/Y domain: range of x-y coordinates
    • Resolution: accuracy in coordinate values
  33. Project tool
    • Defines x-y coordinates system, by adding a new feature and keeping the original data
    • Should be used only with correct coordinate system data
  34. Define projection
    • Changes only the coordinate system labels
    • Use only on data set with Unknown coordinate system
  35. Gnomonic
    light source is at the center of the globe
  36. Stereographic
    light source is at the point exactly opposite the point of tangency
  37. Orthographic
    at a considerable distance (infinite point). Light rays are parallel.
  38. Projections Commonly Used in the US
    • Albers Equal-area Conic
    • Lambert Conformal Conic
    • Transverse Mercator
  39. Albers Equal-area Conic
    • equal-area conic projection
    • Well suited for large countries that mainly east-west in extent
    • Maximum scale error is approximately 1.25% over an area the size of the US.
  40. Lambert (Azimuthal) Conformal Conic
    • Map is conformal, but not perspective, equal-area, or equidistant
    • Distances are true only along standard lines and reasonably accurate elsewhere in limited regions
    • Directions are reasonably accurate, and distortion of shapes and areas minimal at the standard lines
  41. Transverse Mercator
    • A horizontal cylinder
    • Intersects the ellipsoid along a single north-south tangent or two secant lines
    • Has a band of low distortion, runs in a north-south direction
  42. Rectangle coordinate systems
    • Universal Transversal Mercator
    • State Plane
  43. State Plane
    • Used in US
    • Each state in US are divided into several zones
    • Devised by the US Coast and Geodetic Survey
    • Unit: foot
    • FIPS as zone number: e.g. Fips 4021
    • Zone name: e.g. Louisiana South Zone
  44. Reference systems
    • Geoid: shape and size of earth
    • GCS: Geographic Coordinate System
  45. GCS
    • Geographic Coordinate System
    • Small circles: latitude circles other than the equator
    • Grid circles permit to identify the shortest distance
  46. Datum defined by:
    • Coordinate system defines geographic system
    • Ellipsoidal system approximates Earth’s shape
    • Horizontal measures locations on earth
  47. Geoid
    • Three-dimensional surface where the gravity is constant
    • Difference in the density of the Earth cause variation in the gravity force
    • Can be thought of as the level of an imaginary sea
    • Why do we need Geoid?
    •    Elevation is typically the vertical distance to Geoid, also called orthometric height
    •     Height above the ellipsoid is referred to as an ellipsoid height
    •     Geoidal height: orthometric height – ellipsoid height not a mathematically defined surface. It is measured (e.g. using gravimeters) and interpolated.
  48. datum
    a set of parameters defining a coordinate system, and a set of control points whose geometric relationships are known, either through measurement or calculation
  49. ArcGIS vector data formats
    • Coverages
    • Shapefiles
    • Geodatabases
  50. Encoding Grid Cell Value
    • Centroid method: Each cell is assigned the value of the feature that passes through the center of the cell.
    • Predominant type (winner takes all): Each cell is assigned the value of the feature that fills the majority of the cell.
    • Most important type: Each cell is assigned the value associated with the features that have been specified as more important to the study.
    • Edge separated: The ambiguity is solved by marking those cells as Edges
  51. Whittaker-Shannon Sampling Theorem
    • the cell size must be smaller than half of the minimum feature (minimum map units) that you intend to represent.
    • The commonly suggested cell size is 1/5 - 1/7 of the minimum feature to be captured
  52. Bands
    A set of matrices of cells that represent multiple attributes of the same area
  53. Data depth
    • Known as pixel/bit depth
    • How many bits are used to represent one pixel value
    • Affects the data range (integer) and precision (floating point numbers)
  54. NoData
    • Where the phenomenon does not occur
    • Do not confuse with value 0
    • Use some specific values to represent
  55. Advantages of Vector Model
    • Spatial objects are represented based on precise x, y coordinates, and therefore measurements of area, perimeter and distance, and graphic representation are more accurate and precise.
    • Data structure is more compact and less redundant, and thus less demanding for data storage.
    • Besides geometric properties, topological relationships between spatial objects can be explicitly encoded and stored.
    • Support a wide variety of advanced, topology-based analyses and well suited for representing and modeling linear features and network, such as, address geocoding, path-tracing, pavement management, bus routing, emergency response planning, pipeline planning, sales analysis and wildlife management.
    • Encoded topological relationships facilitate error checking in vector database.
    • Easy to do visual overlay analysis. Multiple vector layers can be overlaid together, or draped on top of raster data.
  56. Limitations of Vector Model
    • Complex data structure, and time-intensive data acquisition and input.
    • Computationally intensive and complicated for some spatial operations, such as overlay, calculation of area, neighborhood analysis, etc.
    • Not suitable for representing a gradual change (transition zone) between adjacent units. Many physical characteristics such as soil and vegetation types vary and have ‘fuzzy’ borders.
    • Not suitable for representing continuous surface like terrain. Surface metric properties, like slope aspects, curvature, cannot be easily calculated from contour representation.
    • Incompatible with digital image data. Manipulation and enhancement of remote sensing data are difficult in a vector-based GIS system
  57. Advantages of Raster Model
    • Simple and straightforward data structures-matrix-like 2D array. The easiest format to be dealt with Fortran, C, and other computer languages.
    • Not only support the discrete (categorical) objects but also continuous geographical features. Highly varying surface like terrain can be effectively and efficiently represented in a raster format.
    • Computationally efficient in some types of quantitative analysis: map overlay, map algebra, surface modeling and simulation, such as cut-fill analysis, visibility, watershed modeling, slope and aspect calculation, and three-dimensional display.
    • Compatible to remotely sensed data and photogrammetric data. Traditional digital image processing techniques can be introduced for the manipulations of cell-based raster data.
    • Compatible to modern high speed graphic input and output devices.
  58. Disadvantages of Raster Model
    • Unable to explicitly representing the topological relations, therefore does NOT support network type of analysis.
    • Data redundancy in homogenous areas and corresponding large volume of data.
    • Limited accuracy of location and corresponding area and distance measurements. The resolution and accuracy depends on the size of the grid cells.
    • The output of graphics is less aesthetically pleasing because irregular lines and boundaries tend to be a blocky, jagged, stair-case like appearance rather than the smooth lines.
  59. Triangulated Irregular Network (TIN)
    • The major problem of vector data structure is the representation of continuous surface model such as elevation, precipitation, etc.
    • TIN is a mass-point dataset with lines linking the points and constructing triangles
  60. Data frames
    Boxes containing layers to be viewed and analyzed together
  61. Jenks Natural Breaks
    • The “best” classification method
    • Exploits natural gaps in the data
    • Good for unevenly distributed or skewed data
    • Default method, works well for most data sets
    • Can be very slow if the data has many values
  62. Graticule
    • Spherical grid or geographic grid
    • the network of parallels and meridians on the earth’s surface
  63. Standard line
    • line of true scale
    • The line along which projection surface touches or intersects the globe are called standard lines
    • There is one standard line when a planar surface intersects the globe, or a cone or cylinder is tangential to the globe.
    • There are two standard lines when a cone or cylinder intersects the globe.
    • Along the standard line, the map has no distortion, and the map scale is identical to the nominal globe.
    • In general, geometric distortion increases with the distance to the standard lines.
  64. Azimuthal (direction)
    • A straight line drawn between the central point (standard point) to all other points shows the true great-circle route and azimuthal direction from the central point to all other points.
    • Directions from points other than the central point (standard) to other points are not accurate.
  65. The primary use of the map and desired geometric properties to be preserved
    • Equal-area cylindrical projections are often used to show the world-wide distribution of a variety of geographic phenomena.
    • Presentation maps are usually conformal projections, although compromise and equal-area projections can also be used.
    • Navigational maps are true direction and/or equidistant.
  66. The locations of the area to be mapped
    • Azimuthal projection is often used to map polar region
    • Conic projection is often used to map mid-latitude regions;
    • Cylindrical projection is often used to map equatorial region.
  67. Predominant orientation of the area to be mapped
    • Albers Equal-area Conic, Lambert Conformal Conic are often used to map the countries that are mainly east-west in extent.
    • Transverse Mercator is used to map the states that are mainly north-south in extent
    • Azimuthal projection is better for mapping the area with a circular shape.
  68. The Extent of the area to be mapped
    • As the mapped area increases to sub-continental, distortion becomes a significant problem.
    • As mapped areas become smaller in extent, the selection of the projection becomes less critical. Potential scale errors begin to drop off considerably.
  69. Projections Commonly Used in the US
    • Albers Equal-area Conic
    • Lambert Conformal Conic
    • Transverse Mercator
  70. Albers Equal-area Conic
    • This is an equal-area conic projection having two standard parallels, but not conformal, perspective, or equidistant.
    • Well suited for large countries that mainly east-west in extent.
    • USGS uses 29.5N and 45.5N as the standard parallels to map the conterminous US. Maximum scale error is approximately 1.25% over an area the size of the US.
    • Meridians are straight lines that intersect parallels at right angle. Parallels are concentric circles, making construction relatively easy.
  71. Lambert Conformal Conic
    • Map is conformal, but not perspective, equal-area, or equidistant.
    • Distances are true only along standard lines and reasonably accurate elsewhere in limited regions.
    • Directions are reasonably accurate, and distortion of shapes and areas minimal at the standard lines.
    • Also used to show other countries or regions that is mainly east-west in extent.
  72. Transverse Mercator
    • A horizontal cylinder
    • Intersects the ellipsoid along a single north-south tangent or two secant lines
    • Has a band of low distortion, runs in a north-south direction

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