There are six main methods used to input data in a GIS:
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.
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.
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
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
|Arc||Line feature: a node at each end; vertices at each change of direction.|
|Node||Endpoint of an arc (also found at intersections between lines).|
|Vertex||A point on an arc that signals a change of direction.|
|Pseudo Node||On an (island) arc that connects to itself or where an attribute changes or on a long arc
|Dangling Node||Arc endpoint that is not connected.|
|Label Point||Identifies a point feature or polygon centre.|
|Tic||Geographic control point; features can be registered to the same coordinate system.|
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c. Data are outdated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).
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
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):
(Click on image to enlarge)
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. The data are lines and points, no polygons (limited attributes and completeness)
c. data were collected from aerial photographs in the 1980s
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
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
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)
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