Data Input and Data Source - GIS tutorial dan Remote Sensing of facegis.com
Data Input and Data Source

There are six main methods used to input data in a GIS:

1. Keyboard

This is mostly for attribute data, coordinates are mostly collected by the methods below:

2. Co-ordinate geometry (COGO) 

This is used for high precision municipal data, based on azimuth / distance from known points, rather than a coordinate system. It is not common in natural resources.

3. Global Positioning Systems (GPS)

A growing source of data since the early 1990s: mostly spatial data e.g. new features such as trails, or cutblocks. Attributes can be added during data collection via a data table, or added in the Lab. See Geog205 lecture notes for more details on GPS. Smoothing of lines collected is done using GIS software.

4. Scanning

Scanning produces a raster file that can be used as a background layer for digitising, or if very 'clean' vectors can be directly extracted by automatic 'line following'. Topographic map example

  • Electronic detector moves across image.
  • Flat-bed (up to 11" by 17") and drum (full sheet).
  • Most suitable for continuous image or full map sheet.
  • Creates raster data: 1-8 bit or 24 bit (3 x 8 bit).
  • High resolution generates large storage. - possibly for few features ?
  • Cannot recognize lettering, point symbol design, without sophisticated raster to vector(R2V) software

5. Digitizing

Digitizing is done in two ways:

a. Following lines on maps using either a tablet with map taped down, or onscreen scan: both are 'second hand data' .. although the data on the map were created first hand by photogrammetry and photo interpretation

b. Onscreen interpreted from digital (stereo) photogrammetry  ('first hand data')   (e.g. lab 6 )

Figure 5-1 : Simplified digitizer setup
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Figure 5-2 : Digitizing Terms
Terms Example Description
Arc GIS tutorial dan Remote Sensing of facegis.com Line feature: a node at each end; vertices at each change of direction.
Node GIS tutorial dan Remote Sensing of facegis.com Endpoint of an arc (also found at intersections between lines).
Vertex GIS tutorial dan Remote Sensing of facegis.com A point on an arc that signals a change of direction.
Pseudo Node GIS tutorial dan Remote Sensing of facegis.com On an (island) arc that connects to itself or where an attribute changes or on a long arc
Dangling Node GIS tutorial dan Remote Sensing of facegis.com Arc endpoint that is not connected.
Label Point GIS tutorial dan Remote Sensing of facegis.com Identifies a point feature or polygon centre.
Tic GIS tutorial dan Remote Sensing of facegis.com Geographic control point;  features can be registered to the same coordinate system.

6. Data file import (see below)

A. Introduction- data availability - - the most common input method now

Most GIS topographic data have been created by either :

i. digitizing existing maps or

ii. interpretation of digital aerial photography

1980-1990: digital data were scarce, users had to create their own data   (type i)

1990-2000: data increasing but often unaffordable (type i and ii)

2000s:         increasing data download, but variable based on data provider policy: user pay, free, restricted.

Digital data have become more plentiful, although having data may be affected by:
a. Inappropriate scale for the project .
b. Wrong data type (not the layers needed).

c. Data are outdated

d. A past problem: formats complicated importing into software, solved by: Feature Manipulation Engine (FME).


B. Global data (small scale)

The largest scale for the whole world covered is 1:1,000,000. The 'Digital Chart of the World' (DCW) was created and completed in the early 1990s but is not suitable for larger scale mapping. Digital Chart of the World


C. Federal: NTS (analogue) -> NTDB (digital)

Topographic map data are available in digital form at: 1:50,000 and 1:250,000, from the National Topographic DataBase (NTDB), using the National Topographic System (NTS) index (the maps have been digitised). Saskatchewan, Newfoundland/Labrador and the Territories rely on NTDB data. All provinces are available in 1:50,000, but only some parts of the territories; the largest scale for the whole of Canada is 1:250,000.

Overview of digital mapsheets: http://toporama.cits.rncan.gc.ca ....(also see www.mapplace.ca for BC map sheets) Since 2007, NTDB data became freely downloadable: http://www.geogratis.ca Free Yukon data: http://geomaticsyukon.ca


D. BC 'TRIM' (Terrain Resource Inventory Management) 

The program was complete for the whole province by 1996 primarily at 1:20,000 (by digital photo-interpretation), and also 1:250,000 with federal agreement.   One 1:250,000 sheet contains 100 1:20,000 sheets (see figure below):

Figure 6-1
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(Click on image to enlarge)
Figure 6-2
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The BC Geographic system subdivides each lettered quadrangle into one hundred mapsheets numbered 001 to 100 (Fig. 2) The size of each 1:250 000 quad is 1 degree of latitude by 2 degrees of longitude. 
The size of each 1:20 000 BCGS mapsheet is 6 minutes of latitude by 12 minutes of longitude.

1:20,000 sheet: 12'(longitude) x 6' (latitude) = 7,027 sheets(tiles) for BC [$600/tile]
1:250,000 sheet: 2 degrees longitude x 1 degree latitude = 100 sheets

SOme data are downloadable from www.lrdw.ca

TRIM I  data consist of five 'layers':

    a. Contours (lines for cartographic depiction).
    b. DEM (points for 'analysis' and secondary products, such as hill-shading).
    c. Planimetric (all point features and lines, eg roads, rivers, buildings, etc).
    d. Text.
    e. Control points.
These form the basis for GIS in BC, possibly the best provincial data in Canada, although ...

    a. The data are lines and points, no polygons (limited attributes and completeness)
    c. data were collected from aerial photographs in the 1980s

 
TRIM II (1997- )

The TRIM program was completed in 1996. A second program was commenced (TRIM II) to re-map the province, primarily as an update, but also to improve details for some areas, and to add digital orthophotographs as another layer. The Prince George region was the first completed.

The program is ongoing, currently about 5000 of the 7027 tiles done (see orthophoto layer in lrdw or mapplace).
details at: http://ilmbwww.gov.bc.ca/bmgs/

Online BC TRIM website and links to other provinces: http://maps.gov.bc.ca

 
Ministry of Forests (BC):

Forest cover is available for the province, at 1:20,000 for sheets corresponding to TRIM data. These data are generated from files created in Microstation, used in the Forestry Industry for mapping (as opposed to GIS). Vegetation Resource Inventory (VRI), replacing older forest cover can be downloaded from www.lrdw.ca


E. Municipal

Major cities have online GIS website for viewing data, the Prince George pgmap site has almost 200 layers:

Data conform to UTM coordinates in a 2 x 1km UTM grid.

Layers include 1m contours, street names and numbers, and 2003/2006 colour orthophotography (25cm resolution). For other BC cities, see www.mapplace.ca and click link to 'Other data and map links' (on the left)

F. Canada thematic (census) data

Thematic data are acquired from Statistics Canada. Universities take advantage of the 2001 Data Liberation Initiative http://www.statscan.ca/english/Dli/dli.htm These data are available through the UNBC spatial data librarian.

Satellite (raster) imagery can be downloaded from many sites .. see GEOG432


7. Review

Things you should know after finishing this lecture
  1. Why are small-scale data more often free than large scale data
  2. Why are data directly created from photography likely superior to digitizing maps
  3. What are the largest scales that can be guaranteed for data covering: a. BC b. other provinces c. Territories
  4. Are there up to date topographic data for all BC at large scale ? (and why or why not?)

 

Source: http://www.gis.unbc.ca/courses/geog300/lectures/lect4/index.php