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GIS data encoding

Dr. Huidae Cho
Institute for Environmental and Spatial Analysis...University of North Georgia

1   GIS without data?

Can you imagine GIS without data?

GIS without data is like a car without fuel.

2   Data stream

Data stream includes data encoding and data editing processes.

Analogue data (paper form) must be made digital (computerized) first.

Data encoding and integration can be lengthy because of different types, formats, scales, and resolutions.

data-stream.png

3   Data encoding

Data need to be encoded for GIS being used.

Data encoding is the process of getting data into the computer.

Many methods are available.

Differs by GIS packages.

Data standards help.

3.1   Data encoding methods

Data sourceAnalogue or digital sourceEncoding methodExample
Tabular dataAnalogueKeycoding, text scanningAddress lists of hotel guests
Map dataAnalogueManual digitizing, automatic digitizing, scanningHistorical maps
Map dataDigitalDigital file transferDTM, digital topographic data
Field surveyAnalogueKeycodingNational population census data
Field surveyDigitalDigital file transferData from meteorological station recording equipment
Aerial photosAnalogueManual digitizing, automatic digitizing, scanningSki slope locations
Aerial photosDigitalDigital file transferSki slope locations
GPSDigitalDigital file transferNavigation systems
Satellite imageryDigitalDigital file transfer, image processingForest condition data

3.2   Analogue data

Analogue data must be made digital.

Keyboard entry (keycoding) via keyboard

  • Small data sets and attributes
  • Human errors, typographical errors

Digitizing of paper maps using a digitizing table

  • Reflects topology of features
  • Takes patience and practice
  • Positional errors

3.2.1   Digitizing analogue data

digitizing-paper-map.png

digitizing-results.png

3.2.2   Scanning analogue data

Scanning (automatic digitizing) using a scanner to create a digital raster file of lines (automatic line follower)

  • Faster and easier
  • Expensive equipment
  • Optical distortion
  • Scanning of unwanted information
  • Amount of editing to produce data for analysis can be huge

scanners.png

3.3   Electronic data transfer

Get data digitally if available.

Often reformatting (data conversion) is necessary (e.g., unzip, .e00 file, etc.).

Data collected digitally from GPS receivers, total stations, data loggers, and handheld devices

  • May be transferred wirelessly
  • May be in GIS format by default (Bonus!)

3.4   Obtaining data from other sources

What data are available?

What will the data cost?

How will the data be supplied?

How long will it take to get it?

What format will the data be in?

4   Data editing

Once in GIS, corrections and manipulations are made.

Check for errors

  • Errors in source data
  • Errors from the encoding process
  • Errors propagated during transfer and conversion

Compare with source data

4.1   Common digitizing errors

common-digitizing-errors.png

4.2   Before and after data editing

before-and-after-corrections.png

4.3   Data transformation

Reprojection may be necessary to overlay data spatially.

Common coordinate system must be used.

Data may require transformation.

Scale is only as good as the worst used (smallest scale) – Other data is generalized to decrease unnecessary details and the file size.

4.4   Topological mismatch between data in different projections

different-projections.png

Image source: Courtesy of Peter H. Dana

4.5   Results of repeated line thinning

repeated-line-thinning-1.png repeated-line-thinning-2.png

Image source: The Digital Chart of the World. Courtesy of ESRI. Copyright © ESRI. All rights reserved; (inset): From ESRI, ArcGIS online help system, courtesy of ESRI. Copyright © 2005 ESRI. All rights reserved

4.6   Edge matching

edge-matching.png

4.7   Editing database

Attributes of a database must be maintained and updated to be useful.

In a geodatabase, the existing length and area attributes become updated automatically, but other attributes will need to be updated manually.

  • Can edit values one at a time in the attribute table
  • Can use the Field Calculator to assign a value to a field

5   Geocoding

Geocoding is the process of converting addresses into geographic coordinates.

An address, a zip code, or a place name is used to convert from a non-coordinate system to geographic coordinates.

Address matching is the process of geocoding street addresses to street networks based on address ranges for each street segment.

geocoding.png

5.1   Typical problems in geocoding

  • Address misspelled
  • Different formats (e.g., capitalization)
  • Different abbreviations (e.g., periods or not)

Standards are needed.

6   Reverse geocoding

Reverse geocoding is the process of converting geographic coordinates into addresses.