Overlay Analysis in GIS

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Overlay Analysis in GIS
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• Vector overlay analysis
• Raster overlay analysis

Outline
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Vector overlay analysis

• Dissolve Aggregates features that have the same
  value for an attribute that you specify.
  (polygons)
• Merge Appends the features of two or more themes
  into a single theme. Attributes will be retained
  if they have the same name. (polygons, lines,
  points)

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• Clip Clip themes like a cookie cutter on your
  input theme. The input theme attributes are not
  altered. (polygons, lines, points)
• Intersect two themes Cuts an input theme with
  the features from an overlay theme to produce an
  output theme with features that have attribute
  data from both themes. (polygons)

Vector overlay analysis
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• Union two themes Combines features of an input
  theme with the polygone themes from an overlay
  theme to produce an output theme that contains
  attributes and full extent of both themes.
  (polygons)
• Identity tool Combines the portions of features
  that overlap the identity features to create a
  new feature class.

Vector overlay analysis
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• Update tool Updates the attributes and geometry
  of an input feature class or layer by the update
  feature class or layer that they overlap.
  (polygons)
• Erase tool Creates a feature class from those
  features or portions of features outside the
  erase feature class.

Vector overlay analysis
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• Symmetrical difference tool Creates a feature
  class from those features or portions of features
  that are not common to any of the other inputs.
  (polygons)
• Spatial join tool Joins only the attribute data
  for features of theme 2 to the features of theme
  1, which share the same location.

Vector overlay analysis
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• Intersect Returns any feature that geometrically
  shares a common part with the source feature (or
  features).

• Area within a distance of Creates a buffer (or
  buffers) with a size equal to the distance
  specified around the source feature (or
  features), then returns all the features
  intersecting the buffer (or buffers).

Select by location spatial query
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• Completely contain Each point in the geometry
  of the source feature must fall inside the
  geometry of the target feature, excluding its
  boundaries.

• Are completely within Each point in the geometry
  of the target feature must fall within the
  geometry of the source feature excluding its
  boundaries.

Select by location spatial query
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Raster overlay
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• 2. State Plane
• Many states are devided into multiple zones
• Each zone has its own central meridian and
  standard parallels
• Origin is located in the south of the zone
  boundary, false eastings are applied to have
  positive x and y values
• Boundaries of these zones follow county
  boundaries

COORDINATE SYSTEMS
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• Universal Transverse Mercator (UTM)
• Adopted by the US Army for large scale military
  maps
• Globe is divided into 60 zones between 84S and
  84 N, most of which are 6 wide
• Each UTM zone has its central meridian and spans
  3 east and west from the center of the zone
• The position of the cylinder developable surface
  is positioned at a different place around the
  globe for each zone

COORDINATE SYSTEMS

• x- and y-coordinates are in meters by convention
  of central meridian
• y-orgin is the equator
• X-origin is 500,000 m west

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UTM Zones
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• Datums
• Sets of parameters and ground control points
  defining local coordinate systems
• Earth geoid ? geodesists use spheroids or
  ellipsoids to model the 3-dimensional shape of
  the earth
• Still local variations because of the
  differential thickness of the earths crust, or
  differential gravitation of the crustal material
• Datum is created to accountfor these local
  variationsin establishing the coordinatesystem
• World Geodetic System WGS84
• North American Datum from1927 - NAD27 (fits the
  north-american continent better)

DATUMS and SPHEROIDS
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• Mercator (cylindrical)
• Shape conformal small shapes are well
  represented (maintains local angular
  relationships)
• Area increasingly distorted towards the polar
  regions
• Direction any straight line drawn on this
  projection represents an actual compass bearing
• Distance Scale is true along the equator, or
  along the secant latitudes

EXAMPLES
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• Lambert (planar)
• Shape Shape is minimally distorted, less than 2
  percent, within 15 from the focal point, angular
  distortion is more significant small shapes are
  compressed radially from the center and elongated
  perpendicularly.
• Area equal-area
• Direction True direction radiating from the
  central point.
• Distance True at center. Scale decreases with
  distance from the center along radii and
  increases from the center perpendicular to the
  radii.

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• Mollweide
• Shape Shape is not distorted at the intersection
  of the central meridian and latitudes 40 44' N
  and S. Distortion increases outward from these
  points and becomes severe at the edges of the
  projection.
• Area equal-area
• Direction Local angles are true only at the
  intersection of the central meridian and
  latitudes 40 44' N and S. Direction is distorted
  elsewhere.
• Distance Scale is true alonglatitudes 4044' N
  and S. Distortion increases with distance from
  these lines and becomes severe at the edges of
  the projection.

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• Orthographic
• Shape Minimal distortion near the center
  maximal distortion near the edge.
• Area The areal scale decreases with distance
  from the center. Areal scale is zero at the edge
  of the hemisphere.
• Direction True direction from the central point.
  
• Distance The radial scale decreases with
  distance from the center and becomeszero on the
  edges. The scale perpendicular to the radii,
  along the parallels of the polar aspect, is
  accurate.

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• Albers (conic)
• Shape Shape is true along the standard parallels
  of the normal aspect (Type 1), or the standard
  lines of the transverse and oblique aspects
  (Types 2 and 3). Distortion is severe near the
  poles of the normal aspect or 90 from the
  central line in the transverse and oblique
  aspects.
• Area There is no area distortion on any of the
  projections.
• Direction Local angles are correct along
  standard parallels or standard lines. Direction
  is distorted elsewhere.
• Distance Scale is true along the Equator (Type
  1), or the standard lines of the transverse and
  obliqueaspects (Types 2 and 3). Scale
  distortion is severe near the poles of the
  normal aspect or 90 from the central linein
  the transverse and oblique aspects.

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