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Getting the Map into the Computer

Getting the Map into the Computer. Lecture 4 Introduction to GISs Geography 176A Department of Geography, UCSB Summer 06, Session B. 4.1 Analog-to-Digital Maps 4.2 Finding Existing Map Data 4.3 Digitizing and Scanning 4.4 Field and Image Data 4.5 Data Entry 4.6 Editing and Validation.

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Getting the Map into the Computer

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  1. Getting the Map into the Computer Lecture 4 Introduction to GISs Geography 176A Department of Geography, UCSB Summer 06, Session B

  2. 4.1 Analog-to-Digital Maps 4.2 Finding Existing Map Data 4.3 Digitizing and Scanning 4.4 Field and Image Data 4.5 Data Entry 4.6 Editing and Validation Getting the Map into the Computer

  3. Maps have a communications function but... A map has a storage function for spatial data Somehow, the visually “stored” data must get digital Real and Virtual maps GIS maps are digital not analog

  4. Traditionally most of the cost of a GIS project One time cost Depends on reuse Requires maintenance GIS Data Conversion

  5. Map libraries Reference books State and local agencies Federal agencies Commercial data suppliers e.g. GeographyNetwork.com, Rand McNally, Thompson, NAVTEQ, maps.com Finding Existing Map Data

  6. Existing map data can be found through a map library, via network searches, or on media such as CD-ROM and disk. Many major data providers make their data available via the World Wide Web, a network of file servers available over the Internet. GIS vendors package data with products. Existing Map Data

  7. Commercial vendors

  8. U.S. Geological Survey (USGS) National Oceanic & Atmospheric Administration (NOAA) Census Bureau National Geospatial-Intelligence Agency (NGA) Environmental Protection Agency (EPA) many more... Federal Data Agencies

  9. National Spatial Data Infrastructure http://www.fgdc.gov/nsdi/nsdi.html

  10. Geodata.gov

  11. National Spatial Data Clearinghouse

  12. USGS: National Mapping

  13. National Map Viewer

  14. DOQQ plus DLG streets

  15. DRG plus DLG streets

  16. NLCDB plus DLG streets

  17. Seamless data download

  18. Geospatial Onestop Geography Network EROS Data Center FGDC: Standards Alexandria Digital Library State data centers e.g. Teale in CA MapQuest NAVTEQ, etc. Counties, municipalities, universities, tribes, etc. Other components of the NSDI (Portals, standards, services, data)

  19. U.S. Bureau of the Census

  20. NOAA Weather and other data

  21. Eros Data Center • Distributed active archive center • Sioux Falls, SD • Operated by USGS

  22. US GeoDataftp access toDEMDLGGNISGIRASetc.

  23. GNISFeature locations

  24. GIRASLand Use and Land Cover Data

  25. GIRAS into Arc/Info (GIRASARC)

  26. Terrain dataDEMDLG ContoursDCW Contours

  27. US Federal FOIA COFUR State (e.g. California, Teale Data Center) Local (e.g. Portland, OR Metro) Other countries Protection for security Steganography, watermarks, deliberate error Attributes vs. map data Your Spatial Data “Rights”

  28. CORONA (KH Satellites)Goleta, CA, 1967 Image

  29. Purchased Found from existing sources in digital form Captured from analog maps by GEOCODING GIS data can be:

  30. Geocoding is the conversion of spatial information into digital form Geocoding involves capturing the map, and sometimes also capturing the attributes Necessarily involves coordinates Often involves address matching GEOCODING

  31. The method of geocoding can influence the structure and error associated with the spatial information which results Example: scanning (raster), digitizing (vector) GEOCODING LEAVES A “STAMP” ON DATA

  32. Hand out the Attendance Sheet,U idiot!!

  33. Digitizing Scanning Field data collection Geocoding methods for maps

  34. Captures map data by tracing lines from a map by hand Uses a cursor and an electronically-sensitive tablet Result is a string of points with (x, y) values Digitizing

  35. The Digitizing Tablet

  36. Digitizing • Stable base map • Fix to tablet • Set coordinate system • Digitize control points • Determine coordinate transformation • Trace features • Proof plot • Edit • Clean and build topology

  37. Cursor data entry Secondary tablet (menu/template) Voice command entry Point mode Stream mode (one point / time unit) Distance mode (one point / distance unit) Digitizing

  38. Selecting points to digitize

  39. Slivers Duplicate lines Duplicate nodes Unended lines Gaps Zingers Some common digitizing errors

  40. Places a map on a glass plate, and passes a light beam over it Measures the reflected light intensity Result is a grid of pixels Image size and resolution are important Features can “drop out” Scanning

  41. Flat bed Drum DPI File size Scanning

  42. Scanning example 15 x 15 cm (3.6 x 3.6 km) grid is 0.25 mm ground equivalent is 6 m 600 x 600 pixels one byte per color (0-255) 1.08 MB This section of map was scanned, resulting in a file in TIF format that was bytes in size. This was a file of color intensities between 0 and 255 for red, green, and blue in each of three layers spaced on a grid 0.25 millimeter apart. How much data would be necessary to capture the features on your map as vectors? Would it be more or less than the grid (raster) file?

  43. On-screen digitizing

  44. Isolate layer and capture

  45. Resolve errors

  46. Automatic Raster-to-vector

  47. Rasterization problems

  48. Feature vs. Text

  49. Field data collection

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