grid systems. transverse mercator projection copyright © 2009 by maribeth h. price 3-3 south dakota...
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Grid Systems
Transverse Mercator Projection
Copyright © 2009 by Maribeth H. Price 3-3
South Dakota
Zone 16
Universal Transverse Mercator
• Based on Transverse Mercator (cylindrical) projection• World divided into 60 zones 6 degrees wide• Distortion is minimal within each zone• Maps of different areas use best zone• Best for maps covering small area in one zone
UTM Zones
UTM Pole to Pole
Halfway to the Pole
Using UTM
Using UTM
Using UTM
Three Kinds of North
• True North – Along Meridians• Magnetic North – What a compass detects– Important in field– Not important in most GIS
• Grid North – Along N-S grid lines– Minor importance for compass work– Be aware there’s a difference!– Military uses exclusively
Cautions About UTM• Military maps use two letter codes for each
100-km square, but maps will have information to enable conventional UTM
• With military grid references, number of digits indicates level of precision
• Older maps will sometimes have obsolete grids
• Datum, datum, datum!
Military Grid System
• 45N 89 W = E 342,369, N 4,984,896 Zone 16T• Digraph = CQ• 1 km accuracy = 16T CQ 42 84• 100 m accuracy = 16T CQ 423 848• 10 m accuracy = 16T CQ 4236 8489• 1 m accuracy = 16T CQ 42369 84896
• Ticks on USGS topo map = 342,000, 4,984,000
Where Zones Meet
Why a Grid?Latitude /Longitude Grid System
North varies from place to place on the map
Grid north is always the same direction
Angular units differ in scale between N-S and E-W
Grid scale the same in all directions
E-W angular units vary in scale with latitude
Grid squares are always the same size and shape
Hexadecimal Scale Decimal Scale
Copyright © 2009 by Maribeth H. Price 3-15
State Plane System• States divided into
one or more zones identified by a unique FIPS number
• Uses several types of projections
• E-W zones generally Conic, N-S zones generally UTM
Copyright © 2009 by Maribeth H. Price 3-16
Projections for large scale maps
• Local, city, county maps, smaller states– Projection systems virtually eliminate distortion– Choose appropriate UTM or State Plane zone
Wisconsin State Plane Zones
Wisconsin Grid
Systems
Copyright © 2009 by Maribeth H. Price 3-19
Projections for smaller scales• Distortion is inevitable, so
purpose drives the choice– Equidistant maps when
distances are important– Equal area maps when areas
are important– Conformal or compromise
projections for general purpose maps
Coordinate system names generally indicate the locale and purpose it is optimized for. Use for clues to choice.
Metes and Bounds System
Public Land Survey System• AKA Congressional System• Established 1785• Does not apply to:– 13 Original Colonies– Derivative States (VT, KY, TN, ME, WV)– Texas (Former independent country)– Hawaii (Uses Kingdom of Hawaii system)
• Land Division– 6 x 6 mile townships, 36 sections, quarter sections
USA Public Land Surveys
Non-Congressional
Grids
Before Greenwich
Arbitrary Geography
More Arbitrary Geography
Grid vs. No Grid
Gridded Landscape
Where Wisconsin’s Grid Starts
Where California’s Grid Starts
Section Numbering
Wisconsin Townships
Township Labels
Section Descriptions
Limitations of the
Congressional Land Survey
System
Congressional Land Survey System• Not an accurate grid!• Locations within subdivisions may be
imprecise• Data points used in GIS may be tied to system• Authoritative surveys are forever– French strips in LA, MO, WI– Spanish and Mexican land grants
French Long Lot System
French Long Lot System
California: PLSS and Land Grants
California: PLSS and Land Grants
Oh, Canada• Eastern Canada: Metes and Bounds, Long Lot• Northern Ontario: 6 and 10-mile townships• Western Canada: Dominion Land Survey– Modeled on PLSS– 6-mile townships– Townships numbered N-S with Arabic numerals– Ranges numbered E-W with Arabic or Roman numerals– Road allowances between sections– Sections zigzag from 1 in SE to 36 in NE (Opposite US)– ¼-1/4 sections numbered from 1 in SE to 16 in NE
Dangers of Cheap Work
Missed It By That Much