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170 Cards in this Set
- Front
- Back
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What is GIS?
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using spatial data, putting it into a program, storing, and retrieving data
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What is the computer programs used for?
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storing, queriing, analyzing, and displaying geographic data
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Six components of GIS
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1- Hardware (compt. plotter)
2- Software (operating system/applications) 3- Data (Geographic/Spartial - Nongeographic/aspartial/attribute) 4- Institutional infrastructure (data requierments) 5- Brainware (purpose objectives) 6- Lifeware (human operators) |
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Three Major characteristics of GIS data:
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1- Geographically refrenced
2- Spartial 3- Attribute information |
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Geographically refrenced is?
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absolute location (x,y) (addresses, long/lat)
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Spartial is
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representation of the geometry of features (mapping the shapes)
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Attribute information
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features characteristis (non-spartial)
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Spartial data is broken into two different types:
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1- Raster
2- Vector |
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Raster is for what type of data?
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grid - continuous data
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Vector is for what type of data?
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x,y coordinates - discrete data
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Spartial Data: Point Object
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tree, well, powerpole
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Spartial Data: line Object
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hwy, powerline
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Spartial Data: Area Object
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city limits, watershed
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Spartial Data: surface Object
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chemical spills, vegetation
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Spartial Data: Map Projection
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trasformation from spherical geographic grid to a plane coordinate system
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Spartial data Features: Discrete
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do not exist between observations and are individually distinguishable = vector
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Spartial data Features:
Continuous |
values are distributed without interruption continuously across the surface
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Beginning point of a line is
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node
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middle points on a line
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vertices
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a line is __ dementions
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1 dementional
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an area is __ dementional
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2 dementional
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First and end point is the same to be considered__
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an area
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Topology is what type of spatial model:
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vector model
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Topology is
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spatial relationship between features
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Digital Elevation Model (DEM) is an example of what type of spatial model?
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Raster data structure for this type of model
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Digital Elevation Model is :
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a digital terrain representation technique, where elevation values are stored in raster cells (very useful for hydrological modeling)
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Non Spatial/Attribute Data is recorded in what format?
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this is recorded in Tabular formate
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Four techniques for non spatial/attribute data
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1- Nominal = named (oak, fir)
2- Ordinal = Ordered (good, fair) 3- Interval = on a scale (77', 80 4- Ratio = has an absolute zero (percentage) |
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what type of database is attribute data stored in
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Relational Database stores this type of data
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Relational Database is a collection of what?
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A collection of tables which can be connected to each other by attributes whose values can uniquely identify a record
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The column containing the attribute data stored in the relational database is called?
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key field
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Relational Database makes it easy to do what?
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input, search, retrieve, manipulate, and to output data from one or more tables
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GIS software subsystems (3)
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1- Data Input Subsystems
2- Data Storage & Retrieval 3- Data Manipulation & Analysis |
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What does Data subsystems do:
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collect and process data = GPS co-ordinates
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What does Data Storage and retrieval do
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for storing spatial and attribute data = DBMS
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What does Data Manipulation and Analysis do:
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for analyzing spatial relationships = overlay, buffer, selection
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what makes GIS unique
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it has elements of several related technologies and it uses spatial query and spatial analysis
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what is a map projection
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the transformation of a curved earth to a flat map
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Scientific definition of map projection
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a systematic rendering on a flat surface of the geographic coordinates of the features found on Earth's surface
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Maps are __ dimentional representations of Earth
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2- dimentional
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Traditional projections include:
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cylindrical (Mercator), conic, azimuthal, and elliptical
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A projected coordinate system is based on what:
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geographic coordinate (longitude , latitude)
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what is a geographic coordinate system based on
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a sphere or spheroid
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what is a sheroid
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the approximate shape of the earth
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what is a datum
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the position of the spheroid relative to the center of the earth.
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what does a datum define?
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the origin and orientation of latitude and longitude lines
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what happen to map layers of the same area with different projections?
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Locations on one map layer will not coincide with locations on the other map, and the same features will look different on each layer
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All layers of maps must come from:?
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the same projections = need for projection/re-projection
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What is a projection?
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converting digital maps from latitude and longitude values to two dimensional coordinates
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what is re-projection?
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coveting from one coordinate system to another
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Decimal Degrees (DD) =
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degree + minute/60 + second/3600
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what are the three families of map projections?
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1- Azimuthal (flat surface)
2- Cylindrical (cylinders) 3 Conic (cones) |
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Azimuthal map projection can be shown in what ways?
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polar, equatorial, or oblique
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Cylindrical Projections can be shown in what ways?
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normal, transverse, or oblique
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Conic Projections can be shown in what ways?
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Tangent or secant
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Map projections are grouped by their what?
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preserved properties
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What are Azimuthal preserved directions?
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all directions are shown correctly relative to the center.
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what are azimuthal projections frequently used for?
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used for mapping the polar regions
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What are equidistant preserved directions?
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preserves distances accurately in one direction
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What are azimuthal projections used for?
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used for preserving distances
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What do Equal-area or Equivalent projections preserve?
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preserves area
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what is equal-area or equivalent projections important for?
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it has correct earth surface areas and it is important for mass balances
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What are conformal or orthomorphic projections preserved directions?
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preserves shapes (angles) - local angels are shown correctly
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what are conformal or orthomorphic projections used to represent?
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represents mid-latitude regions in either the northern or southern hemispheres
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A planar coordinate system is defined by?
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a pair of orthogonal (x,y) axes drawn through an origin
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What are the types of coordinate systems?
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Universal transverse mercator (UTM), State plane coordinate system, and Public land survey system (PLSS).
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what is the Universal Transverse Mercator (UTM)?
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a global system developed by the US Military services
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what is the state plane coordinate system?
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civilian system for defining legal boundaries
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what is the public land survey system?
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established in 1785 as a method of land subdivision for the US
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In the Universal Transverse Mercator each zone has what?
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Central Meridian
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In the Universal Transverse Mercator each zone has a Central Meridean... give information about them:
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zones are 6 degrees wide, go from pole to pole. 60 zones cover the earth from East to West (6 degrees * 60 = 360 degrees)
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State plane coordinate system is defined for?
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each Sate in teh United States
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EAST-WEST (texas) sates use what type of state plane coordinate system?
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Lambert Conformal Conic
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NORTH-SOUTH (CA) sates use what type of state plane coordinate system?
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Transverse Mercator
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state plane coordinate system has greatest accuracy for?
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local measurements
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Public Land survey system uses what for a basic unit of measurment
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1 acre
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Public Land survey system section =
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each equare mile of an area
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Public Land survey system uses 6 by 6 sections to make what>
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townships
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Public Land survey system is a what
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land subdivision system for the US established in 1785
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What are the two commonly used map projetions
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1 transvers mercator and 2 Lambert conformal conic
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what does transvers mercator (cu;omdrical) projection preserve?
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preserves local shapes (conformal) and directions (azimuthal)
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What does lambert conformal conic (conic and secant) projection maintain?
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samll shapes, preserves directions accurately
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false northing / easting does what
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makes everything positive
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Use points and their coordinates to do what?
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build spatial features
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What are the three steps in the develp process?
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1- use point, line, and area to get shape
2- express (store) the relationship b/w features (topography) 3- create (design) a data structure to allow manipulation of the features and their relationships |
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what is data structure?
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smiple means of depicting spatial phenomenon in a single map environment- logical structure of data files that allows their manipulation by the computer
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what is a data model?
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more complex versions- accommadate interactions b/w database objects (expression of relationships b/w features) Link entities & attributes. Allows analysis of multiple map layers
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what is a georelational data model?
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stores spatial and attriblutes data seperately
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what is spatial data?
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location and geometry in graphic file
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Adv. of georelational data model:
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-less data intensive- good for discrete data
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Dis. of georelational data model:
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-requires combination of spatial and nonspatial (attribute) info
-hared to analze spatial relationships and requires special algorithms to do analysis |
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what is topology?
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studies properties of geometric features that remain invarienat under certain transformations such as bending or stretching
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Topology expresses the spatial relationships b/w features:
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-adjacency (from node to node)
-incidence (arc from or to node) -connectivity (arc connect at node) -area definition (series of connected arc) -contiquity (direction, right & left) |
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What is a topology data model?
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a vector data model that aims at retaining spatial relationship by explicittly storing their info using models as building blocks.
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Topology points can be:
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nodes= that mark start and end points of arces
vertices= pts that define the shape of the line |
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The basic logical feature for a line and area coverage is a
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line segment
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Each individual line segment is defined by
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the coordinates of its end pts called nodes
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Topological info is stored by recording:
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1-the from-node & to-node of each line segment
2-the left-polygon & rt polygon (in the direction of the from-node to the to-node) of each line segment |
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Adv of topology data model
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error check, faster when doing spatial analysis
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Triangulated Irregular Networks (TIN) is a
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vector model representing surfaces
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TIN represents surfaces with:
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a set of (non-overlapping) triangles
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Two basic data Elements of TIN:
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-point with eevation values
-line connecting the point to form triangles |
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The data structure of TIN includes:
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-the triangle numbers and the number of adjacent triangles
-file containing the points, and the edges |
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Dynamic Segmentation model:
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combines a line data to linear measurement systems to represent different scenarios along lines features
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Dynamic Segmentation model includes:
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sections, routes, and events (point event or linear event)
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In object orientated data model the object is:
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something in the software that has a set of properties and can perform operations upon requests
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Object orientated data model produces by___
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classes
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Object orientated data model properties are
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inheritances, Encapsulation, Polymorphism
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Object orientated data model is grouped by:
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-association (b/w 2 objects =car and road/graph and spread sheet)
-aggregation(diff. levels that make up structure) -generalization (simplifying common things) -instantiation -specialization |
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Adv. of Object orientated data model:
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application using objects are easier to customize using an OOP language
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The Geodatabase model is
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an object oriented data model for ArcGIS 9.x
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The Geodatabase model data structure stores:
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both spartial and attribute data in a single database (access, Oracle)
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Adv. of The Geodatabase model:
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eliminate the complexity of coordinating disparate data stores, speeds up the process of retrieval and storage, has the properties of object: inheritance, Polymorphism, encapsulation
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Entity Relationship Diagram is a graphical technique for:
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the digital representation of real world features (entities) and the relationships among them
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Characteristics of The Object Oriented systems:
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inheritance, encapsulation, and polymorphism
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Inheritance characteristic of Object oriented systems is:
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define a generic Object "park" attributres of Park: ownership, rules
Specific parks inherit attributes of object park and add their own (location) |
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Encapsulation characteristic of Object oriented systems is:
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all knowledge about bixon (its size, roaming areas, behavior) are encapsulated in the object "bison"
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Polymorphism characteristic of Object oriented systems is:
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same name, different functions (eg. Migration is different for Bison of different regions)
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Accuracy tells us:
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how close the location of a feature on a map is to its true ground location- affected by map scale and data collection instrument
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Resolution tells us:
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cell size of grid, length of the smallest feature that can be seen and/or recorded (for raster data)
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Precision tells us:
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measures how exactly loction information are recorded (with how many significant digits)
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where do you get GIS data?
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GIS data can be created or preexisting data can be aquired from a remote location
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Popular locations of GIS data in US can be found from:
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clearing houses, geographic networks, and private companies
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The Federal Geographic Data Committee (FGDC) is:
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a national and international attribute and geospartial data standards... supports the NSDI
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The US Geological Survey (USGS) is:
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a major provider of data in the US Topo maps, hydrographic maps, boundaries, road networks, and land use and land cover data
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The US Bureau of census is:
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provides the topologically integrated geographic encoding and refrenced (TIGER) database: administrative boundaries, roads, RR, streams, waterbodies, powerlines, and pipelines
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A Metadata is:
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a file containing info. about the spartial data *very import!
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Metadata content standards (developed by FGDC) are:
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identification, data quality, organization info, spartial refrence, attribute info, way of distribution, and reference info
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Data conversion uses:
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uses tools in GIS application to convert data from one format to another ex. shapefile to coverage
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Data conversion: Neutral format=
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dedicated format data exchange ex. Public eg- DLG (provided by USGS) SDTS =spartial data trasfer standard
*mandatory for federal agencies |
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Four techniques to create new digital data:
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1- digitizing (on screen/using digitizing tablet)
2- scanning 3- remote sensing (raster data) 4- GPS (vector data) (coordinate system) |
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Digitizing
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the process of capturing in compt. form (digital form) info stored in a hard copy map. using a digitizing table/tablet
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tic marks provide:
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geographic registration (min 3 required)
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Three impt. tasks of tic marks:
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1- convert to real world coordinates
2- relocate map between digitizing sessions 3-co-register different maps to the same coordinate system |
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Affine trasformation is
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scale, rotate, translate, skew
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geometric transformation:
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from digitizer unites to real world coordinates
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Estimate of transformation error is provided by:
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the Root Mean Square (RMS) error (the closer to zero=less error on map/ closer they are the better, the smaller they are is good!
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The Root Mean square measures:
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the deviation between the actual location of the control points, as projected from their longitude and latitude readings in the output map and the estimated location as estimated on the input map.
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The number of points (vertices) needed depend on what?
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the complexity of the line
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Streaming is:
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moving the mouse and letting the computer add points every few minutes
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Under sampling results in:
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positional error and not adding enough points
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Over sampling results in:
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waste of time, storage space, and can cause error (adding too many points)
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How do we get polygons?
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derived from a set of ARCs that close (ending and beg. points are the same)
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Double line encoding causes:
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slivers and redundant spatial information
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Common digitizing problems:
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undershoot and overshoot
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snap distance does what?
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corrects undershooting automatically (if line is smaller than snap distance then the line are joined together)
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Fuzzy tolerance is:
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if you inadvertently digitized a line twice, the software will combine them into a single line
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fuzzy tolerance only works if:
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it is set greater than maximum gap distance
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Spatial data editing consists of:
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cleaning (removing errors) and updating data
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spatial data editing includes:
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line simplification, line smoothing, transfering of map features b/w maps, edge, matching and building topology making pieces fit (seaming the edges)
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Where do errors come from?
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digitzing process, changes in real world, application of general procedures with preset parameters (updating process is the same as fixing errors)
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Two major types of errors:
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Location and topological
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Location error is:
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concerns the location of features and their geometry on a map
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Location error includes:
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missing feature, duplicated features, features in wrong location, inaccurate geometry or shape
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location error originates from:
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human errors, error in scanning and tracing, geometric trasformation (tic marks)
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location human errors include:
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missing lines, wrong shape, wrong location, duplicate lines
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location error scanning and tracing errors include:
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interactions, lines that are:too close/wide
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Topological error(logical inconsistencies) violate:
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the topological relationship used in a GIS package or misrepresent the realative positions of features
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Topological errors include:
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undershoot, overshoot, and resulting dangling arc, and dangling node, pseudo node, sliver polygons
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A topology based GIS software can:
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build topology, detect and display, topological errors, assis in removing all errors, assist in digitizing, assist in map feature editing
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A non topological GIS software can be used only for:
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assist in digitizing, assist map features editing
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Steps in topological editing:
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1- build topological
2- select and display topological errors 3- remove errors (using global or local methods) 4- build topology again |
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Errors in snapping distance:
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min. distance b/w 2 nodes
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errors in dangle tolerance
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(dangle lenght) - min. lenght for dangling area
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errors in fuzzy tolerance
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min. distance b/w vertices (along an arc or along 2 arc next to each other) (can remove sliver polygons)
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errors in edge matching
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connecting 2 adjacent maps to make one map (merge in the geoprocessing extension or Arcview and arcmap) needs to be checked for mismatch
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some map feature manipulations
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line simplifications, line densification, line smoothing
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line simplifications
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generalizes a line by removing some of its vertices
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line densification
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adding pt to a line at regular interval
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line smoothing
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adding point to a line by mean of mathematical functions in order to smooth its boundaries (spline function in Arcinfo
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