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Published byNeal Riley Modified over 8 years ago
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Data Sources and Input Historic datasets and maps Modern collection methods
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GPS Trilateration Signal (Radio) Carriers: 1575.42 (L1) and 1227.6 (L2) MHz Codes: Coarse/Acquisition (C/A) and Precision (P) Frequency modulation carries binary sequence Receiver code compared to transmitted code Speed of light*time difference= distance https://www.youtube.com/watch?v=3lNtav3CjM8 http://www.colorado.edu/geography/gcraft/notes/gps/gps.html
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The Good Old Days
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The Bad Old Days Digitizing centuries of hand-drawn maps… Guess who got to do this job?? – Prisoners – GIS Techs – Students!
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Digitizing Digitizing is done in two ways: a.Tracing lines on maps initially using a tablet with map taped down, or onscreen / ‘heads-up’ (= copying a map) – > 1995
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Digitizing Procedure Lines = connected points – Manual point selection – Timed point selection – Interval point selection http://forum.imagej.net/t/digitizing-contour-map/118
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Simplifying Lines Each vertex has a storage cost How much is enough? Too many? If too many, simplify in post process – Point remove: maintain essential shape – Bend simplify: maintain “important” bends http://pro.arcgis.com/en/pro-app/tool-reference/cartography/how-simplify-line-works.htm
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Digitizing Table Technology Mechanical arm—magnetic or physical – Lowest precision; 1960s Linear microphones – Sparking in cursor – Ambient noise introduces error Wire grid with magnetic field – Precision +/- 0.1mm
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Digitizing Costs Labor $ – Technicians (high) – Laypeople (medium) – Prisoners (presumably lower but not low) Equipment $ – $500-5,000 for a digitizer Time – +/-1 boundary per minute
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Sources of Error Precision: – If points +/- 25m on creation – If +/- 25m error introduced on digitization – Conceivably 50m total error Accuracy: – Paper may have shrunk, stretched or torn – Symbols rearranged to prevent overlap – Map sheet boundaries – Human boredom, fatigue, humor or malice
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Input Error: Nature of the Beast Does not cause error messages in analysis Outlier analysis sometimes catches mistakes Easily goes unnoticed until publication
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Digitizing Tables in Modern Practice Take a close look at Scott’s workbench…
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Scanners and Cameras High resolution raster 8,000X10,600 pixels (this model) https://www.youtube.com/watch?v=G7MjUrReUM4 http://www.library.unt.edu/digital-projects-unit/scanners-and-scanning-systems
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Automatic Feature Recognition ArcScan toolbar in ArcMap Automated, semi-automated, manual Must be georeferenced Toolbar:
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Modern Digitizing Error +/- 0.1mm precision from digitizing table – Difficult to confirm questionable points – Error potential depends on scale – 0.1mm on 1:10,000 map less than 1:1,000,000 +/- 0.025mm precision from scanning – Less potential for user bias – Can be checked later if issues arise – Superior precision + accuracy – Lower operational cost
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b. Onscreen from digital photography ('first hand data') – post 1985
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Air Photo Interpretation Stereoscopic Imagery – Contour lines – Slope angle – Elevation + Height http://www.nrcan.gc.ca/earth-sciences/geomatics/satellite-imagery-air- photos/satellite-imagery-products/educational-resources/9395 http://www.geog.ucsb.edu/~jeff/11 5a/lectures/stereoscopy_and_height _measurement.html
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Modern Stereoscopy Done on desktop computers – Setups vary – Far less headache-inducing
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Air Photos for Stratified Sampling Looking for distinct, uniform areas Crown size (age), harvest history Hardwoods (gray) and softwoods (green)
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Stratified Sampling Generate sample points randomly X points per area, e.g. 1 point every 3 hectares Each point tied to polygon = unique stand
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Stratified Sampling: Population A B C D E
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Digitising – editing is still needed : updates and errors Coordinate locations are based on underlying georeferencing e.g. NAD 1983 Edits: e.g. adding new features, modifying existing features, creating a new layer ArcEdit: https://www.youtube.com/watch?v=6dY3x-5qX6Uhttps://www.youtube.com/watch?v=6dY3x-5qX6U
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Snapping Automatic connection to other features – Any features, selected features, feature class – Same feature class (roads) Prevents slivers and disconnects User-defined tolerance, radius… https://blogs.esri.com/esri/arcgis/2010/09/20/using-snapping-effectively-in-arcgis-10/
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Aside: Toolbars Snapping, Editing, GPS, Georeferencing, Draw, Scan, Advanced Editing, etc. plus downloaded add-ins Access via: Customize>Toolbars
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Autotrace Snap an entire line to another line/feature Follows established border precisely Or follows at an offset http://www.lutraconsulting.co.uk/blog/2014/02/11/finger-tired-from-digitising-try-autotrace/ https://blogs.esri.com/esri/arcgis/2010/11/04/getting- the-most-out-of-editing-in-arcgis-10-tracing-features/
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File Conversion FME Universal Translator – GIS Lab has a license ArcMap File formats – Read-only – Read + Write Raster: http://desktop.arcgis.com/en/arcmap/10.3/manage-data/raster-and-images/supported-raster-dataset-file-formats.htm http://desktop.arcgis.com/en/arcmap/10.3/manage-data/raster-and-images/supported-raster-dataset-file-formats.htm Vector: http://desktop.arcgis.com/en/arcmap/10.3/manage-data/datatypes/about-geographic-data-formats.htm http://desktop.arcgis.com/en/arcmap/10.3/manage-data/datatypes/about-geographic-data-formats.htm QGIS: https://docs.qgis.org/2.2/en/docs/user_manual/working_with_vector/supported_data.html https://docs.qgis.org/2.2/en/docs/user_manual/working_with_vector/supported_data.html
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GPX File Conversion GPX is a standard GPS file format QGIS reads it directly ArcGIS has one intermediate step – Conversion tools>From GPS>GPX to Features – Input from GPS, output to shapefile
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Rubber Sheeting Distortion to match-up boundaries Precision + accuracy sacrificed Best to re-check imagery http://hds.essex.ac.uk/g2gp/gis/sect43.asp
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Keyboard Data Entry Spreadsheet --> Attribute Table Spatial reference: GPS –GPS point # = row ID # (“Join” function) Row ID links spatial and tabular data –Field data usually entered in Excel or similar –GPS data straight to Arc
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Keyboard Data Entry 2 Coordinates + all data in spreadsheet Geographic data, no projection (unless…)
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Keyboard Data Entry Tip Speak cells on enter tutorial Speak cells by row/column Tutorial http://www.device42.com/benefits/
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Data Dictionaries (1) Trimble and other survey/map grade GPS Establish database design first – Features may be culverts, bridges, signs, poles… – In this case, poles: http://support.windenvironmental.com/knowledgebase.php?article=106
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Data Dictionaries (2) Populate attributes while collecting points – Takes ~90 seconds to average enough points – Data entry taken care of at no additional time cost Attribute table ready to use Requires proper prior planning http://support.windenvironmental.com/knowledgebase.php?article=106
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One Bear’s Movement > Remote transfer Proximity transfer Direct transfer
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Data Acquisition in 2016 Data BC ESRI Open Data GeoDiscover Alberta BC MoFLNRO GeoGratis Prince George Google Spatially referenced 99% of the time Most data publicly available (no $$)
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Canadian Data Sources Canada: https://www.mcgill.ca/library/find/maps/geospatial-onlinehttps://www.mcgill.ca/library/find/maps/geospatial-online BC: https://catalogue.data.gov.bc.ca/datasethttps://catalogue.data.gov.bc.ca/dataset Alberta: https://geodiscover.alberta.ca/geoportal/catalog/main/home.pagehttps://geodiscover.alberta.ca/geoportal/catalog/main/home.page Saskatchewan: https://www.isc.ca/Pages/Content%20Gallery/GeoSask.aspxhttps://www.isc.ca/Pages/Content%20Gallery/GeoSask.aspx Manitoba: http://www.manitoba.ca/iem/geo/gis/index.htmlhttp://www.manitoba.ca/iem/geo/gis/index.html Ontario: https://www.ontario.ca/page/land-information-ontariohttps://www.ontario.ca/page/land-information-ontario New Brunswick: http://www.snb.ca/geonb1/e/DC/catalogue-E.asphttp://www.snb.ca/geonb1/e/DC/catalogue-E.asp Nova Scotia: https://geonova.novascotia.ca/https://geonova.novascotia.ca/ Quebec: https://www.mcgill.ca/library/find/maps (Gov’t data in a non-ESRI format)https://www.mcgill.ca/library/find/maps Yukon: http://www.geomaticsyukon.ca/http://www.geomaticsyukon.ca/ Northwest Territories: http://www.geomatics.gov.nt.ca/dldsoptions.aspx (must register)http://www.geomatics.gov.nt.ca/dldsoptions.aspx Nunavut: http://ntilands.tunngavik.com/maps/http://ntilands.tunngavik.com/maps/
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U.S. and Other Data Sources NASA: http://data.giss.nasa.gov/http://data.giss.nasa.gov/ Census Data US Geological Society Wikipedia’s List of GIS Data Sources
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Searching the Web: Keywords Google tips and tricks Shapefile British Columbia Wildfire
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Publicly Available KMLs Sometimes Google Earth is all you get It’s enough… – It comes in like this: – Right click Polygons>File>Export data>Export as shapefile – Result: usable shapefile/attribute table (turn off extra items)
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Shapefiles One “shapefile” = 3 or more files.shp: shape format/geometry.shx: shape index format (file navigation).dbf: attribute data (the ‘spreadsheet’).prj: projection data.sbn,.sbx,.fbn,.fbx,.ain,.aih,.ixs,.mxs,.atx,.shp.xml,.cpg,.qix: other formatting filesother formatting files ALL HAVE TO MOVE TOGETHER
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Geodatabases Layers in one place, ready to use + move Pros: functionality, transferability within Arc Cons: proprietary format = unreadable – Some newer software is getting around thatnewer software
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Shapefile/GDB Layer Input Add data from file Polygon Line Point Table Raster Geodatabases Shapefiles (+text)
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Shapefile/GDB Layer Input Add data from ArcGIS Online
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Shapefile/GDB Layer Input Catalog Tab Inside ArcMap Click + Drag to Table of Contents ArcCatalog Click + Drag to ArcMap Table of Contents Add using ArcCatalog or Catalog Tab
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WMS Layer Input Add data->GIS Servers->add WMS Server “Get Layers”
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Layer Files Layer file stores symbology Where the files are How to display them Which attributes to display/hide Does NOT include the data itself Add to map just like a shapefile
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Paper Towns: False Input Agloe, New York Copyright “trap” Agloe General Store Beatosu (Beat OSU) and Goblu (Go Blue) https://www.buzzfeed.com/krystieyandoli/welcome-to-the-agloe-general-store-come-back-soon?utm_term=.gy73AQXmy#.xdyE4mx8j
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Summary Digitizing tables are mostly out Scanning, raster to vector is in Keyboard data entry is still big… always? File conversion remains critical – Digitized in 2002, file format…? Use FMEFME Countless data sources available Input gets easier by the day BUT is still the worst source of error
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