GIS Geographic Information System

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GISGeographic Information System

• Cluster 1
• CPAS

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What is GIS?

• Geographic Information System (GIS) is a system
  of computer hardware, software, and procedures
  designed to support the compiling, storing,
  retrieving, analyzing, and display of spatially
  referenced data for addressing planning and
  management problems. In addition to these
  technical components, a complete GIS must also
  include a focus on people, organizations, and
  standards.

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Three Views of a GIS

• The Database View A GIS is a unique kind of
  database of the worlda geographic database
  (geodatabase). It is an "Information System for
  Geography." Fundamentally, a GIS is based on a
  structured database that describes the world in
  geographic terms.
• The Map View A GIS is a set of intelligent maps
  and other views that show features and feature
  relationships on the earth's surface. Maps of the
  underlying geographic information can be
  constructed and used as "windows into the
  database" to support queries, analysis, and
  editing of the information.
• The Model View A GIS is a set of information
  transformation tools that derive new geographic
  datasets from existing datasets. These
  geoprocessing functions take information from
  existing datasets, apply analytic functions, and
  write results into new derived datasets.

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The Database View
The Map View
The Model View
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GIS data

• GIS data All themes within a GIS are based on
  geographically referenced data, or spatial data.
  GIS software generally consist of two types of
  spatial data (vector and raster data) but can
  also accommodate other components of spatial
  data, such as attribute data and metadata.
• Spatial data
• vector data (feature themes) - attribute data
• raster data (image themes, grid themes) -
  attribute data
• Metadata (data about the spatial data)

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Types of Spatial Data

• Feature themes use vector data, which are
  represented by points, lines, or polygons (e.g.,
  earthquakes, elevation contours, etc.). Some
  feature themes have several polygons associated
  with one or more features and/or features that
  "overlap" one another sometimes referred to as a
  "region".
• Image themes use raster data, which are
  represented by an array of square pixels or
  cells. Each cell has a value associated with it
  that represents a condition found at the
  corresponding location or area of the
  "real-world". Aerial photography and satellite
  imagery are common raster data.
• Grid themes also use raster data but require
  special GIS software to utilize them for spatial
  analyses. The land cover data layer used in GIS
  is a grid that has a spatial resolution of 28.5
  meters, which means that each pixel represents a
  28.5 meter x 28.5 meter area of the "real world."
  In this case, each cell has one of 19 possible
  values that correspond to the 19 different
  classifications (e.g., clear water, alder, open
  conifer forest, and background).

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Raster data

• In its simplest form, a raster consists of a
  matrix of cells (or pixels) organized into rows
  and columns (or a grid) where each cell contains
  a value representing information, such as
  temperature. Rasters are digital aerial
  photographs, imagery from satellites, digital
  pictures, or even scanned maps.

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Vector data

• The vector data model represents each feature as
  a row in a table, and feature shapes are defined
  by x,y locations in space (the GIS connects the
  dots to draw lines and outlines). Features can be
  discrete locations or events, lines, or polygons.

• Most vector geographic information systems
  support three fundamental geometric objects
• Point A single pair of coordinates.
• Line Two or more points in a specific sequence.
• Polygon An area enclosed by a line.

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Land Cover Layer
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Attribute data

• Attribute (tabular) data is the descriptive data
  that GIS links to map features. Attribute data is
  collected and compiled for specific areas like
  states, census tracts, cities, and so on and
  often comes packaged with map data.

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Metadata

• Metadata are essentially "data about data." They
  are an integral part of the spatial data in that
  they describe the content, quality, and other
  characteristics of the spatial and attribute
  data.

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Map Legend

• A map legend defines how colors, symbols,
  contours, and annotation are used in a map.
  ArcView allows users to edit map legends to
  control presentation, and thus interpretation, of
  the data that are displayed.

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Map Features

• Map Features Locational information is usually
  represented by points for features such as wells
  and telephone pole locations, lines for features
  such as streams, pipelines and contour lines and
  areas for features such as lakes, counties and
  census tracts. Point feature A point feature
  represents as single location. It defines a map
  object too small to show as a line or area
  feature. A special symbol of label usually
  depicts a point location. Line feature A line
  feature is a set of connected, ordered
  coordinates representing the linear shape of a
  map object that may be too narrow to display as
  an area such as a road or feature with no width
  such as a contour line. Area feature An area
  feature is a closed figure whose boundary
  encloses a homogeneous area, such as a state
  country soil type or lake.

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Map Characteristics

• In addition to feature locations and their
  attributes, the other technical characteristics
  that define maps and their use includes
• Map Scale
• Map Accuracy
• Map Extent and
• Data Base Extent

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Map Scale

• Map scale indicates how much the given area has
  been reduced. For the same size map, features on
  a small-scale map (11,000,0000) will be smaller
  than those on a large-scale map (11,200).
• Cartographers often divide scales into three
  different categories.
• Small-scale maps have scales smaller than 1
  1,000,000 and are used for maps of wide areas
  where not much detail is required.
• Medium-scale maps have scales between 1 75,000
  and 1 1,000,000.
• Large-scale maps have scales larger than 1
  75,000. They are used in applications where
  detailed map features are required.

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Map Resolution

• Map resolution refers to how accurately the
  location and shape of map features can be
  depicted for a given map scale. Scale affects
  resolution. In a larger-scale map, the resolution
  of features more closely matches real-world
  features because the extent of reduction from
  ground to map is less. As map scale decrease, the
  map resolution diminishes because features must
  be smoothed and simplified, or not shown at all.

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Map Accuracy

• Many factors besides resolution, influence how
  accurately features can be depicted, including
  the quality of source data, the map scale, your
  drafting skill and the width of lines drawn on
  the ground. A fine drafting pen will draw line's
  1/100 of an inch wide. Such a line represents a
  corridor on the ground, which is almost 53 feet
  wide.

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Types of Information in a Digital Map

• Three general types of information can be
  included in digital maps
• Geographic information, which provides the
  position and shapes of specific geographic
  features.
• Attribute information, which provides additional
  non-graphic information about each feature.
• Display information, which describes how the
  features will appear on the screen.

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• Feature Colors and Linetypes should be chosen
  to make the map's meaning clear.
• Naming Roads are important for proper map
  interpretation. This information should be
  legible, positioned in the center of the road or
  offset from the center, and drawn at intervals
  suited to the scale of the final map or its
  purpose.
• Landmark Symbols should be used to indicate
  landmarks, such as hospitals, schools, churches,
  and cemeteries. The symbols should be sized
  appropriately in relation to map scale.
• Polygon Fill Polygon features, such as lakes or
  parks, should be filled with an appropriate color
  or hatch pattern.
• Zoom Layer Control should be set up so that
  detailed, high-density information only appears
  when the user zooms in for a close-up of part of
  the map. For example, when a large area is
  displayed, only the major roads should appear
  for a smaller area, both major and minor roads
  should appear.

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Layering

• Most GIS software has a system of layers, which
  can be used to divide a large map into manageable
  pieces. For example, all roads could be on one
  layer and all hydrographic features on another.
  Major layers can be further classified into
  sub-layers, such as different types of roads -
  highways, city streets, and so on. Layer names
  are particularly important in CAD-based mapping
  and GIS programs, which have excellent tools for
  handling them.

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Types of Digital Maps

• Topographical Maps
• It is a reference map showing the outline of
  selected man-made and natural features of the
  earth. It often acts as a frame for other
  features Topography refers to the shape of
  surface represented by contours or shading. It
  also shows lands, railway and other prominent
  features.
• Thematic maps Thematic maps are an important
  source of GIS information. These are tools to
  communicate geographical concepts such as Density
  of population, Climate, movement of goods and
  people, land use etc. It has many
  classifications.

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GPS

• Global Positioning System is a system of
  satellites, computers, and receivers that is able
  to determine the latitude and longitude of a
  receiver on Earth by calculating the time
  difference for signals from different satellites
  to reach the receiver.