Finding GIS Data

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Finding GIS Data?

• (CEONet) Canadian Geospatial Data Infrastructure
• (SEDAC) Socio-economic data applications center
• (EOSDIS) Earth Observing System Data Gateway
• (FGDC) Federal Geographic Data Committee
  Geospatial Data Clearinghouse
• Data availability from national geospatial
  databases
• North Carolina Geographic data clearinghouse
• Other Data Source Links

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Secant Map ProjectionIn this example the
cylindrical surface used for the map cuts the
globe at the maps representative fraction.
Along this line there is distortion free mapping
of the geographic space.
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Converting DDMMSS/DD

• Degree to Decimal Degree
• Latitude (DD, MM, SS) 050 30" 40'
• Decimal degree (DD.dddd) 5(30/60)(40/3600)
  5.5111
• Decimal Degree to Degree
• Decimal degree (DD.dddd) 5.5111
• Consider 60 minutes 1 degree, 60 seconds 1
  minute
• DD. (degrees) 5.5111 50
• MM (minutes) 0.5111
• 5111 degrees/10000 x 60 minutes/1 degree
  30.666 minutes
• SS (seconds) 30.666
• 666 minutes/1000 x 60 seconds/1 minute 39.96
  or 40 rounded up

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Coordinate Systems Spatial Referencing

• Spherical Coordinate Systems
• Geographical coordinate system (Longitude
  Latitude)
• Rectangular Coordinate Systems
• UTM (Universal Transverse Mercator)
• UPS
• State Plane
• Non coordinate systems
• US Public Land Survey (rectangular survey system)
• US Postal Codes

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Universal Polar Stereographic Grid (UPS)

• Rectangular coordinate system for polar regions
  (areas not covered by UTM system)
• Covers areas between the 80 degree parallels
  poles. (applied to the Earth's polar regions
  north of 840 N and south of 800 S.
• The eastings and northings are computed using a
  polar aspect stereographic projection
• Zones are computed using a different character
  set for south and north Polar regions.

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image source http//www.survivaliq.com/navigation
/grids_par3.htm
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North Polar Area UPS Grid
image source http//www.ncgia.ucsb.edu/education/
curricula/giscc/units/u013/figures/figure20.gif
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South Polar Area UPS Grid
image source http//www.ncgia.ucsb.edu/education/
curricula/giscc/units/u013/figures/figure21.gif
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U.S. Public Land Survey

• Not really true coordinate system type of land
  partitioning system (rectangular survey system)
• A cadastral survey (relating to land boundaries
  and subdivisions developed as a basis for
  taxation)
• The USPLSS applies to most of the U.S. except for
  the thirteen original colonies, Texas, and
  Hawaii. 
• based on the establishment of principal meridians
  and baseline that intersect each other at right
  angles.

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(USPLSS)
Image source http//www.hbcollege.com/geography/r
egionalatlas/planegrid.html
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(PLSS Twnshp)

• The pink square in the diagram refers to one
  township, which is equal to 36 square miles. Each
  square then approximates a one mile square area
  or (640 acres).

image source http//www.hbcollege.com/geography/r
egionalatlas/planegrid.html
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(PLSS Twnshp cntd)
Each one-mile-square area can then be referenced
by township location relative to the baseline and
principal meridian. In the diagram above, the
highlighted township is located on the second
township east of the principal meridian, thus its
location is (R2E). The highlighted cell is also
the third township south of the baseline, which
positions the township at (T3S). The collective
coordinates for the township would be T3S/R2E,
which represents a 36 square mile area.
image source http//www.hbcollege.com/geography/r
egionalatlas/planegrid.html
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(PLSS Sections)

• Sections, approximately one mile square, are
  numbered from 1 to 36 within a township.
• Fractional units of section quarters, designated
  as numbered lots, often result from irregular
  claim boundaries, rivers, lakes, etc.

http//www.colorado.edu/geography/gcraft/notes/coo
rdsys/coordsys_f.html
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(PLSS Twnshp divisions)
Each township can then be divided down to a
smaller area. In this diagram, one of the
township grid cells has been broken down to
halves and quarters. Each cell represents 640
acres, or 1 square mile. The southwest quarter of
the northeast quarter (SW1/4 of the NE1/4) of the
1 square mile grid has been identified, which
represents a 40-acre area. By reducing townships'
areas, you can identify and map individual
property lines. In the United States many
property lines are still referenced using this
method.
image source http//www.hbcollege.com/geography/r
egionalatlas/planegrid.html
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Reading PLSS codes
Tutorial on Reading PLSS Descriptions
image source http//www.hbcollege.com/geography/r
egionalatlas/planegrid.html
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Miscellaneous Systems

• Postal codes such as the United States ZIP code
  can be used to identify areas.
• Three digit codes identify large areas.
• Five-digit ZIP codes identify smaller areas.

Find ZIP Codes for any location in the United
States
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How to Read the Universal Transverse Mercator
(UTM) Grid
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Review

• For a projection, what is a line or point of
  least distortion?
• What does this point or line represent?
• What happens as to data accuracy as one moves
  away from the point or line of least distortion?

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Review Coordinate Systems

• Coordinate systems are used on maps. They provide
  the x and y values that indicate spatial
  position.
• The x and y values given to any location are
  determined by
• ellipsoid datum selected
• coordinate system selected
• coordinate system zone
• USGS maps portray two different coordinate
  systems and up to 4 zones

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Review Common Coordinate Systems

• UTM (Universal Transverse Mercator)
• Global coordinate system divides world into 60
  zones
• Zones run in N/S columns of 60 each
  labeled by numbers 1-60
• Rows represent E/W direction of 80 each
  labeled by letters C X (omits I O)
• Measuring unit -- normally in meters
• Each zone has its own central meridian
  arbitrarily set at 500,000 meters

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Review Common Coordinate Systems

• SPCS (State Plane Coordinate System)
• Rectangular coordinate system for the U.S.
• 120 zones US, PR US Virgin Islands
• Each state has at least 1 zone each zone has an
  arbitrarily set origin (normally west then south
  of southwestern most point on map)
• 3 projections used-depends on direction of state
• Lambert Conformal Conic for states longer in E/W
  direction
• Transverse Mercator for states longer in the N/S
  direction
• Oblique Mercator for panhandle of Alaska
• Measuring unit -- feet

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Review Coordinate Systems Origins

• Each coordinate system works with ONE projection
  system
• Most common
• Transverse Mercator
• Lambert Conformal Conic
• Each coordinate system has its own unique origin
  or reference point

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Review
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