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Spatial Data

Spatial Data. What is it? Where does it come from? How is it different? Where can I get it? Where is it?. Where does it come from?. 1970s – put map on board and trace stuff desired Boring! Currently? Aerial photographs Satellites USGS quads Google trucks . What is it?.

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Spatial Data

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  1. Spatial Data What is it? Where does it come from? How is it different? Where can I get it? Where is it?

  2. Where does it come from? • 1970s – put map on board and trace stuff desired • Boring! • Currently? • Aerial photographs • Satellites • USGS quads • Google trucks

  3. What is it? • Any data that has location in it. • Some examples that don’t • Usually arranged in thematic layers • Town boundaries • Roads • Rivers and streams • Lakes • Etc.

  4. How is it different? • From what? Paper maps • Stored in Computer as thematic layers • Roads, boundaries, streams, lakes etc. • Dynamic – easily edited • Variable viewing scale • Can easily be used to make paper maps when needed (Google, Mapquest) • Are not static

  5. Where can you get it? • Lots of places! • CUGIR • NYS Clearing house • Federal web sites • National Map • EPA • Forest Service • See http://www.esf.edu/git/SUPPORT.htm

  6. The where is it… • How do we locate Syracuse in space on the earth’s surface? • On a FLAT surface? • We can’t Xerox it! • Math

  7. Syracuse -76.19 W 43.07N -76.19 degrees west of meridian through Greenwich, England 43.07 degrees N of the equator • How do we locate Syracuse on earth?

  8. North Pole Lat = 30º Long = -6 0º Lat = 0º Lat = -30º  SouthPole Earth’s Coordinate System X is Longitude and is measured E and W from Greenwich, England. West is negative, East is positive Y is latitude and is measured N and S from the equator. North is positive and S is negative. These are called Geographic Coordinates

  9. 43.07 degrees N of the equator -76.19 degrees west of meridian through Greenwich, England

  10. -76.12° 43.08° W76.15° N43.04° X, Y = Longitude, Latitude 90E, 30N +90, +30 90 60 30 Equator 0 -30 -60 -90 -30 90W, 30S -90 -180 -90 0 +90 +180 Lines of constant Longitude Lines of constant Latitude

  11. The world in Geographic Coordinates Is Antarctica Really that big?

  12. The where is it… • How do we locate Syracuse in space on the earth’s surface? • On a FLAT surface? • What we just did, plot Long, Lat coordinates, put the globe on a flat surface but  DISTORTION • Why distorted?

  13. Oops! Can't flatten a Sphere Without distortion

  14. Problem #1, Datums • First step – a basis for spherical coordinates • BUT Earth is NOT a sphere! It is pear shaped • To accommodate this geographers and surveyors have created models of the earth’s surface • These are called Datums • And this is booby trap #1 because… • Different shapes  different coordinates

  15. Some Datums NAD 27 NAD 83 WGS 84 • These are the common datums • For Coordinate Systems the spatial properties are given in statements like… NAD_27_UTM _ZONE_18N NAD_83_SPC _ZONE_4826

  16. Step & Problem #2 • Have model of earth’s surface • Now have to mathematically project ~ spherical coordinates onto a flat map • This is called Projection • All spatial data not on ~ sphere has both a datum and a Projection.

  17. Mercator

  18. The Projection Problem • There are many mathematical ways of projecting the spherical surface onto a flat surface. • For the earth these have names like Albers equal area Mercator Albers Peters Polyconic Lambert equal area Azimuthal

  19. Other Projections Which is Right? Wrong Question – they are all right, just different. And they all have different properties

  20. And then there are Coordinate Systems • The UTM (Universal Transverse Mercator) coordinate system • Globe sliced into 60 “orange slices” numbered 1 to 60 • The State Plane coordinate system • Depends on state • These are the systems you will usually be using.

  21. Most of NY is in UTM Zone 18 UTM Zones

  22. NY East Zone 4801 State Plane Zones NY Central Zone 4826 NY West Zone 4851 Transverse Mercator NY Long Island Zone 4876 Lambert Conformal

  23. Coordinate Systems Coordinates • Coordinate system coordinates are • Northings (Y) – units N of origin of zone • Eastings (X) – units E of origin of zone • Units (usually) • UTM – meters • SP - feet

  24. UTM coordinates for CCC 4,756,000m N Of Equator NORTHING NAD27_UTM_ZONE_18_N 373,800mE EASTING

  25. Problem #3 Geographic SCALE

  26. Scale = distance on map (distance unit)distance on ground (same distance unit) Definition A Scale of 1/24,000 means 1 inch (or foot, or furlong) on the map = 24,000 inches (or feet or furlongs) on the ground. Scale is also an indication of horizontal accuracy of data 25K ~40’, 50K~80’, and so on.

  27. 3.5” 2,600 Mi Numeric or Ratio scale =1/47,067,429

  28. Living Room Dining Room Kitchen 2.6” / 25’ Scale = 1/115

  29. Small Scale dataLarge area/sheetLeast accurate Large Scale dataSmall area / sheetMost accurate Living Room Dinning Rm. Kitchen Scale 1/47,000,000 =0.000000021 Is a smaller number than 1/46,000 =0.000022 Is a smaller number than 1/115 =0.008696

  30. Problem #4 -Accuracy & Generalization • When a paper map is made at a very small scale the cartographer is limited by the pen being used • Can’t draw anything finer than the width of the pen line. • At a scale of 1/1,000,000 a line 0.05 cm wide = 0.05x1,000,000 cm or 50,000 cm or 500 meters or 19,850” or 1,640’ wide! • What road is 1,640’ wide!!! • So on the map the road is much, much too wide

  31. Accuracy & Generalization • Take the case of a winding stream • Shrink it to a Smaller scale (large area, small paper • Now it is hard to see what is there • So the cartographer simplifies the stream

  32. The generalized stream is not as accurate a representation of the stream as the original And if you try to mix data of different scale common lines are NOT going to match Original Generalized Accuracy & Generalization Error!

  33. Problem #5 • The Coincident Line Problem • Becomes a problem when you try to combine different layers of geo data. • Boundaries etc. do NOT line up • Can be very frustrating!!!

  34. Booby Trap Summary • Datum • Projection • Scale • Generalization • Coincident lines • Using a GIS is more than just combining various data layers – just knowing what buttons to push is NOT sufficient!!! • You have to be careful that the basic 5 booby traps outlined above do not cause problems • And 5 possible sources of error give Murphy a field day since problems encountered go up as n2 n

  35. How do you know? • A complete data set has • Spatial Attributes • Datum • Projection • Scale of source data • Other data about the layer – and lots of it assuming your data has metadata METADATA DATA ABOUT DATA

  36. ESRI to the rescue! • As long as the data you have has metadata ArcMap will display all the data correctly even if they have different spatial properties! • Called “Projection on the fly”

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