Mapping Your Data

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Mapping Your Data

• Christopher Martin
• csmartin_at_buffalo.edu

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Data Models

• Two primary data models used when making maps
• Raster Data
• Vector Data

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Raster Data

• Consists of discrete cells (think graph paper)
• Each cell has a discrete value
• Occur in rows and columns
• Examples
• Images (all image types)
• DEM

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Vector Data

• Each position is represented by coordinates
• Coordinates are connected to form lines or
  polygons
• Points, lines and polygons are then used to
  represent geographic features
• Examples
• Shapefile

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Points, Lines, Polygons
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Data Sources

• US Census Bureau
• Not just population data
• Generalized Boundary Data
• ESRI
• TIGER/LINE
• NED Data
• FEMA Q3 Flood Data
• USGS
• SEAMLESS Distribution

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Data Sources (contd)

• NYS GIS Clearing House
• Membership required
• Wide variety of data
• CUGIR
• NYS and National data
• Free, huge variety
• CIGAR
• Worldwide Elevation Data
• Columbia University EDS
• Electronic Data Service

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Data Sources (contd)

• Geography Network
• Aggregates data from different providers
• Online Map Server Available

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Data Quality

• Meta Data
• Data about the data
• All legitimate providers will provide this
• Available for download or online viewing

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Map Scale

• The ratio between the distance on the map, and
  the distance in real life
• ALWAYS expressed in terms of 1
• Usually a ratio
• E.g. 1100000, 110000
• Other scales are available
• Visual scale is the second most common

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Coordinate Systems

• Two types of coordinate systems used in geography
• Spherical (Latitude and Longitude)
• Typically not used in ArcGIS
• Always used in Google Earth
• Rectangular
• Predominantly used in Arc and GIS in general
• UTM - Universal Transverse Mercator
• State Plane
• Other countries have their own.

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Spherical Coordinate System

• Based on meridians and parallels
• Latitude (parallels)
• Measured northward or southward from the equator
  to poles
• Ranging 0-900 north or south
• The measuring units are degrees, minutes, and
  seconds, 10 60 and 160
• The length of one degree latitude is similar
  everywhere, 111km/69miles
• Longitude (meridians)
• Measured eastward or westward from the Prime
  Meridian at Greenwich, England to the
  International Date Line
• Ranging 0-1800 east or west
• The measuring units are the same as Latitude
• Length of one degree longitude reduces toward
  poles

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Rectangular Coordinate Systems

• Convert the curved surface of the earth onto a
  flat surface
• Standard cartesian coordinates, but different
  names
• X is called Easting
• Y is called northing

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Universal Transverse Mercator

• Based on the mercator map projection
• Divides the world into 60 zones
• Starts at 180 degrees longitude
• Each zone is 6 degrees of longitude wide
• Labeled 1-60 going eastward
• And 20 Rows
• Labeled C-X, skipping I and O
• Intersection of Row and Zone is a Quadrangle
• Usually referred to as quad
• Measurement unit is meters

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Universal Transverse Mercator
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State Plane

• Used exclusively in the United States
• The US is divided into 120 zones
• Follow state and county lines
• Each state has its own map projection
• North to South states use Mercator
• East to West states use Lambert Conformal Conic

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State Plane
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So What?
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Map Projections

• A way to convert coordinates from spherical
  (earth) to flat (map)
• Projections define how to to transform the
  spherical coordinates to flat ones
• They are NOT map coordinates
• Classified two ways
• By the surface projected onto
• By what gets distorted

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Surfaces

• Developable Surfaces
• What kind of shape will we use?
• It has to be 2D, and we need to be able to
  unroll it
• The earth gets wrapped in the shape, and the
  surface is transferred to the 2D shape
• Types
• Cylindrical, Conic, Azimuthal

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Cylindrical Projections

• Mercator
• Transverse Mercator

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Azimuthal Projections

• Top down view
• Or Bottom Up

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Conic Projections

• Used to focus on a particular continent
• Least amount of distortion for east-west direction

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Distortion Projections

• All maps distort
• Its inevitable
• Projections can be grouped based on WHAT is
  distorted
• Conformal - shapes are the same
• Equal-Area - areas are the same
• Equidistant - distances are the same

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Projection Example
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Measuring Distortion
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Comparisons of Projections

• Map Projection Poster

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Map Types

• Thematic Maps
• Not reference maps
• Four main types
• Choropleth Map
• Proportional Map
• Isarithmic Map (contour)
• Dot Map

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Choropleth Map

• Shaded Areas
• The color of the shade varies based on
  measurement of our variable

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Isarithmic Map

• Also known as Contour Maps
• We draw lines to connect separate variables that
  have the same value

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Proportional Symbol Map

• Uses symbols
• The size of the symbol varies according to the
  variable

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Dot Density Map

• Uses dots
• Size is uniform, but the concentration represents
  changes in the variable

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Cartograms

• Are NOT maps
• Area is not preserved
• Area of the geographic regions varies by variable
• Two primary types
• Area
• Area gets larger or smaller depending on the
  variable
• Distance
• Nodes or places can be closer or farther
  depending on realtive distance

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Cartogram
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File Formats

• Shapefile
• A collection of points, lines and polygons
• Tabular data values assocated with each
• DEM
• Raster data, each cell represents elevation
• Comes in different resolutions

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Getting to Know ArcGIS

• ArcMap
• Your main tool. Handles map layout, projection,
  data classification, analysis
• ArcCatalog
• Asset management program. Maps drives of data for
  easy access, displays meta data, manages database
  connections
• ArcView
• Older version of ArcMap.
• ArcScene
• 3D rendering

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Your friend, the Shapefile

• A Misnomer
• More the one file
• Vectors in one file
• Data in another
• Index in another
• Optionally a projection file