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Gistutorial for Health Lecture 4 Projecting and Using Spatial Data

Gistutorial for Health Lecture 4 Projecting and Using Spatial Data. Lecture 4 Outline. Map Projections Coordinate Systems Map Scales and Units GIS Data Data Sources Linking GIS Layers to Internet Sites. Map Projections. Map Projections and Distortion.

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Gistutorial for Health Lecture 4 Projecting and Using Spatial Data

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  1. Gistutorial for Health Lecture 4 Projecting and Using Spatial Data

  2. Lecture 4 Outline • Map Projections • Coordinate Systems • Map Scales and Units • GIS Data • Data Sources • Linking GIS Layers to Internet Sites

  3. Map Projections

  4. Map Projections and Distortion • Map projections produce distortion in one or more spatial properties: • Shape, area, distance, and direction • Specific projections eliminate or minimize distortion

  5. Distortion Examples

  6. Mercator Projection: Distortion

  7. Robinson Projection: Distortion

  8. Projection Important • Measurements used to make important decisions • Comparing shapes, areas, distances, or directions of map features • Features and images are aligned New York New York Los Angeles Los Angeles Projection: MercatorDistance: 3,124.67 miles Projection: Albers Equal AreaDistance: 2,455.03 miles Actual distance: 2,451 miles

  9. Projection not Important • Business applications • Not of critical importance • Concerned with the relative location of different features • On large scale maps - street maps • Distortion may be negligible • Map covers only a small part of the Earth's surface

  10. Coordinate Systems

  11. Coordinate Systems • Spherical/Polar • Geographic Coordinate System • Rectangular • State Plane • UTM

  12. Geographic Coordinate System

  13. Geographic Coordinate System • Latitude and Longitude • Census Bureau TIGER files Geographic Coordinate System Grid

  14. Longitude: Meridians

  15. Latitude: Parallels

  16. Origin • Longitude (prime meridian) 0 • Latitude (equator) 0

  17. Coordinates Pittsburgh 40 -80

  18. Pittsburgh’s Point • Degrees, Minutes, and Seconds (DMS): • 40°26’2”N latitude • -80°0’58”W longitude • Decimal Degrees (DD) • 1 degree = 60 minutes, • 1 minute = 60 seconds • 40°26’2” = • 40 + 26/60 + 2/3600 = 40 + .43333 + .00055 = • 40.434°

  19. Translated to Distance • World circumference through • the poles is 24,859.82 miles, • so for latitude: • 1° = 24,859.82/360 = 69.1 miles • 1’ = 24,859.82/(360*60) = 1.15 miles • 1” = 24,859.82*5,280/(360*3600) = 101 feet • Length of the equator is 24,901.55 miles

  20. Rectangular Coordinate Systems

  21. Rectangular Coordinate Systems State Plane Coordinates • Local Governments UTM • US Military Rectangular Coordinate System Grid

  22. 400 (400, 300) North (Feet) 200 (100, 200) 0 0 200 400 East (Feet) Rectangular Coordinates • Has all positive Cartesian coordinates in feet, called false eastings and false northings

  23. State Plane Coordinate System • Established by the U.S. Coast and Geodetic Survey (now the National Ocean Survey) • At least one for each state • Rectangular (x,y) coordinates • 125 zones, following state and county boundaries each with its own projection: • Lambert conformal projection for zones with east-west extent • Transverse Mercatorprojection for zones with north-south extent • Cannot have zones joined to make larger regions

  24. State Plane Coordinate Zones

  25. State Plane Coordinate Zones

  26. City of Pittsburgh as Geographic Coordinates

  27. City of Pittsburgh as State Plane Coordinates

  28. Universal Transverse Mercator System (UTM) • NIMA - Military grid system • Based on the transverse Mercator projection • Applied to maps of the Earth's surface extending from the Equator to 84 Degrees north and 80 degrees south latitudes

  29. UTM Zones in the Contiguous United States World is divided into 60 north-south zones, each covering a strip 6° wide in longitude

  30. Map Scales and Units

  31. Dimensionless Map Scales • ratio that relates a unit of measure on a map to some number of the same units of measure on the earth's surface • 1:25,000 • tells us that 1 unit of measure = 25,000 of the same units on the earth's surface • 1” on the map = 25,000 inches on the earth's surface • one meter or one yard or one kilometer or one mile would represent 25,000 meters or yards or kilometers or miles, respectively, on the earth's surface.

  32. Small Scale Map Large Scale Map Large and Small Scale Maps 1:5,000 is largescale 1:50,000,000 is small scale

  33. Map Units Feet or meter is the map unit for many local government GIS applications

  34. Map Units Inch is the map unit for CAD applications

  35. Scale 1:100,000 Scale

  36. Scale 1:24,000

  37. Scale 1:10,000

  38. Scale 1:2,000

  39. GIS Data

  40. GIS Data • ArcInfo Coverages • ArcView Shapefiles • CAD Files • Aerial Photos • Event Files

  41. AAT Arc Attribute Table ARC Arc coordinates and topology BND Coverage minimum and maximum coordinates CNT Polygon centroid table PAL Polygon topology PAT Polygon/Point Attribute Table TIC Tic coordinates and Ids DBF Database Table ArcInfo Coverages

  42. ArcINFO Coverages in ArcMap

  43. Coverage Attribute Table Polygon Coverages • Area and perimeter automatically calculated Line Coverages • Length automatically calculated

  44. B E 1 2 Pine St. 733 A 734 F C Oak St. 3 4 D G ArcInfo Coverages • Advantages • Many feature types • Polygons share borders • Automatic Area/Perimeter/LengthFields • Disadvantages • Cannot edit in ArcMap

  45. ArcInfo Export files • .e00 export exchange file • ArcCatalog translates into ArcGIS • Creates coverages

  46. ArcView Shape Files • Advantages • heads-up digitizing and editing • less storage/rapid display • can export to CAD • Disadvantages • one feature type • no area or perimeter with new shapefiles

  47. ArcView Shape Files • From 3 to 5 Files • .shp - stores feature geometry • .shx - stores index of features • .dbf - stores attribute data • .sbn and .sbx - store additional indices

  48. ArcView Shapefiles

  49. CAD Files • Why CAD Drawings? • Better Precision for Digitizing • .DWG / .DXF

  50. Adding CAD Files

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