Lecture 2 Map Projection, Datum

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Lecture 2 Map Projection, Datum

• GPS and Digital Map
• Everything in Digital GPS itself is relying on
  digital technologies.
• Fast to transfer and process
• Digital maps can be made faster and cheaper, also
  more accurately
• Availability of mapping software and hardware

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Digital Map and GPS

• Why digital maps are useful for GPS?
• Finding addresses quickly
• To show where are you
• Locating nearest service center
• To show driving directions for somewhere you
  want to go
• To correct your GPS data collections
• To create maps
• To help/guide you through the GPS data collection

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Finding Your Data

• Where you can find the data you want?
• Search over internet with google or yahoo
• You can also use data finder services
• gis.unc.edu
• terraserver-usa.com
• geographnetwork.com
• Library, Government Website etc.

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Typical Map Data

• Topographic Maps (Digital Raster Graphics - DRG)
  have contour lines that trace the outline of the
  terrain and show elevation.
• The most popular topographic maps for use within
  the U.S. are made by ___
• The topo maps that show the most detail are
  sometimes called quad sheets or 7.5 minute maps.

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Typical Map Data (Cont.)

• TIGER Topologically Integrated Geographic
  Encoding and Referencing data.
• TIGER data is free (www.census.gov)
• DLG Digital Line Graph
• Township and Range has been used since the
  1790s to survey public lands in the united
  states. (PLS)

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Typical Map Data (Cont.)

• MrSID (Multiresolution Seamless Image Database.
  It is a file format (.sid) developed and
  patented by LizardTech.
• Graphics in SID format are compressed with a
  lossless compression algorithm.
• DOQ (Digital Orthophoto Quadrangle) are aeiral
  or satellite photography that has been corrected.

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Typical Map Data (Cont.)

• ESRIs Map data shapefile, coverage, GRID,
  geodatabase.
• ERDAS Imagine IMG
• AUTOCAD DXF
• http//en.wikipedia.org/wiki/GIS_file_formats

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Where We Are?

• Coordinate Systems
• A map datum is a mathematical model that
  describes the shape of an ellipsoid (the earth).
  Some examples
• Clark 1880, 1886
• NAD 27, NAD 83
• Qornoq
• Djakarta

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WGS84

• World Geodetic System of 1984 (WGS84) based on
  the GRS ellipsoid virtually identical with the
  NAD83. WGS84s previous version is WGS72.
• Prior to NAD83, the most popular datum in U.S.
  was NAD27, based on parameters determined by
  Clarke in 1866.

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These examples are two common world spheroids
used today with their values rounded to the
nearest meter. For each spheroid, the difference
between its major axis and its minor axis is less
than 0.34 percent.
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Map Projections
(a) Azimuthal (b) Cylindrical (c) Conic. Light
source positions, also called perspective
positions, play an especially important role in
planar projections. (Different aspects, such as
polar, equatorial, or oblique, will also affect
the map projection)
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Map projections distortion

• The conversion of geographic locations from a
  spherical coordinate system to a flat surface
  causes distortion. The projection process will
  distort one or more of the four spatial
  properties listed below. Distortion of these
  spatial properties is inherent in any map.
• Shape
• Area
• Distance
• Direction

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The Universal Transverse Mercator Coordinate
System

• UTM projection has been used by several
  coordinate systems
• Part of the civilian UTM system USGS, 1977
• Part of the state plane system (SPC)
• And the military grid
• It has been used for mapping
• Most of United States
• Many other countries
• The planet Mars

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State Plane Coordinate System