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Georeferencing with Paper Maps

Georeferencing with Paper Maps

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Georeferencing with Paper Maps

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  1. Georeferencing with Paper Maps • Map Basics • How to Georeference with Paper Maps • Latitude and Longitude Mathematically • Error Calculator

  2. Pros and Cons of Paper Maps Pros • Some features, such as topographic contours may only be found on printed maps. • Old paper maps may be the only option for obtaining coordinates for historic localities • Expedition maps may be annotated with exact locations of events. Cons • Time-consuming • Good quality paper maps may be hard to find • Map printing errors (sometimes intentional)

  3. Map of Canada’s Wonderland, N of Toronto, Canada

  4. Map Basics • Projection • Map Anatomy: • Scale • Grid • Datum • Citing Map as Georeferencing Source

  5. Projection • A map projection is a method used to convert a 3D surface into 2D. • All methods involve compromises to preserve area, linear distance, or shape.  • Which compromise is right?

  6. Projection Geographic preserves NS distance Mercator preserves shape (terrible for poles, distorts area)

  7. Projection Winkel Tripel (NGS solution): reduced distortion in both area and distance

  8. Projection “Butterfly” map – Cahill 1909 • Emphasis on symmetry • Preserves area, shape • Contiguous land masses

  9. Projection: Regional Squat California (Geographic) vs. Equal-Area California (Teale Albers)

  10. The Paper Map

  11. Map Anatomy: Map Scale

  12. Map Anatomy: Map Scale • Usually recorded as a ratio, such as 1:100000, or a fraction, such as 1/100000 • Large scale maps, such as 1/10000, show finer detail, less area • Small scale maps, such as 1/500000, show less detail, greater area • Think of large and small scale as how big the fraction is. • Example 1/10000 > 1/500000

  13. Map Anatomy: 1:25000 Large Scale

  14. Map Anatomy: 1:250000

  15. Map Anatomy: 1:500000

  16. Map Anatomy: 1:1000000 Small Scale

  17. Map Anatomy: Grid

  18. Map Anatomy: Grid Map with no grid

  19. Map Anatomy: Grid • Can have more than one grid system on a map (e.g., UTM and latitude and longitude) • Shows placement of parallels and meridians • Maps without grids cannot be used to determine coordinates – only extents

  20. Universal Transverse Mercator

  21. The Grid UTM Northings UTM Eastings

  22. Map Anatomy: Datum Map with no grid labeled

  23. Map Anatomy: Datum • Usually found near the map scale or publisher’s name • Use Horizontal Datum, not Vertical Datum • If ellipsoid is given instead of a datum then one can choose a comparable datum using the pdf document found at http://earth-info.nga.mil/GandG/publications/tr8350.2/wgs84fin.pdf(Use Appendix B)

  24. Georeferencing Source Data • For georeferencing, sources should include: • Publisher name • Map Date • Map Scale • Map name • Examples: • USGS 15’ Topographic Series Boone 1956 • USGS Topoquad 1:24000 Key West 1962

  25. Paper Maps • Paper often have more detail than other sources • Especially useful for distances by roads and topographic features like rivers and mountain ranges • Pay special attention to the grid lines and the hemisphere when reporting in decimal degrees

  26. Coordinate Signs for Hemispheres

  27. Determining Coordinates from Paper Maps: Ye Olde Method Nauru Island, Pacific Islands Geographic Society, 1960 1:12,000

  28. Determining Coordinates from Paper Maps: Latitude

  29. Determining Coordinates from Paper Maps: Latitude S

  30. Determining Coordinates from Paper Maps: Longitude

  31. Determining Coordinates from Paper Maps: Longitude E

  32. Determining Coordinate Precision Determining Coordinate Precision for the Georeferencing Calculator: The smallest measurement using our rulers is 1 mm ( = 0.1 cm), therefore we need to convert millimeters to minutes: 0.1 cm x (2 minutes/14 cm) = 0.014 min Choose the next largest fraction of a minute on the calculator. For 0.014 minutes, select 0.1 minutes.

  33. Determining Coordinates from Paper Maps: Error Calculation

  34. Determining Coordinates from Paper Maps: The Georeferencing Calculator Method Locality Description: Bebedero We need: • One set of known coordinates • Measuring tool

  35. Determining Coordinates from Paper Maps 1. Find locality and known coordinates.

  36. Determining Coordinates from Paper Maps 2. Measure distance in both directions from the known location to the center of the named place. 118 mm East X 83 mm North

  37. 3. Use calculator to convert map measurements to real-world distances.

  38. 4. Calculate to determine new coordinates

  39. 5. Verify new coordinates

  40. 6. Promote coordinates to make the named place a new starting point.

  41. 7. Use calculator to determine error only.

  42. 8. Account for measurement error.

  43. 9. Calculate for coordinate uncertainty (Max. Error).

  44. In Conclusion • Pay attention to cardinal directions and hemispheres • Measure from the center to the edge of the feature to get the extent • Plot your coordinates to double check your work • Explain any decisions you had to make in the georeferenceRemarks field • Explain any errors in the locality description in the locality errors field

  45. For Georeferencing Source be sure to include the following: • Publisher name • Map Date • Map Scale • Map name • Example: United States Geological Society (USGS) Topographic Map California, 1956, map scale 1:24,000, map name “Boone” • Determining Lat and Long: Determining Coordinate Precision: 0.1 cm x (2 minutes/14 cm) = 0.014 min Round up to 0.1 minute precision