What are the main data sources for GIS? Do some research and try to list Canadian sources (with their web addresses) for road data.
Geographical Information System or GIS is a database system that have the capacity of analyzing spatially referenced data (ESRI). Any data with spatial attributes can be a source of GIS. Several processes in GIS are encoding, storage, processing and display of digitized maps (Understanding GIS). Some of the Canadian websites that share free data are the Canadian GIS and Geomatics, ESRI Canada, National Resources Canada, GeoBase, GeoGratis, and some other Canadian websites that offer open data. These provide information about Canada’s map with administrative boundaries, Digital Elevation Data, geodetic network, geographic names, land cover, National Hydro Network, National Road Network, Satellite Imagery (GeoBase).
GeoGratis is one of the most useful websites in Canada for it has several links like Geospatial Data Extraction, GeoGratis Catalogue, Toporama Interactive Map, GeoGratis Index, and GeoGratis Search. All of the data available here are free of charge and can be used without any restriction. ESRI, in general, provides not only spatial data but also applications in order to fully analyze the information about a certain place that will serve a certain purpose. Some of those applications are ArcGIS, ArcMap, ArcHydro, etc.
ArcGIS is the whole package of the GIS-based applications developed by ESRI up to this date. ArcMap is used in order to layout spatial data with their corresponding attributes and analyze the relationship between the layers and the entities inside the data given. The final product is to make a visual representation of these results, which is a map. ArcHydro deals with datasets from water management, flow networks, and all the other water bodies and finding the relationship of each other to one another.
What is meant by slope and aspect?
Slope is the incline or steepness of a surface (ESRI GIS dictionary). It’s basically the ratio of the rise over run. Aspect can be derived from the elevation of continuous surfaces because it identifies the steepest downslope direction of a face for TIN face, and the steepest downslope direction of a plane for a raster cell. In map projections, aspect refers to the conceptual center of a projection system (ESRI GIS dictionary).
Scale is the ratio between the distance on the map and the corresponding distance on the ground, depending on the units used (ESRI GIS dictionary). In mathematics, as well as in the “real world,” points can be represented as a single smallest unit in a plane. Lines, on the other hand, are consisted of continuously connected set of points. Finally, polygons can be represented as the result of interconnected lines. According to the statement, the distinction between the three terms is one only of scale. It meant that from points, one can create a line (a unit with a higher scale than points) just by adding more points, then can be further made into a polygon (a unit with a higher scale than lines) by adding more lines. In geodetics, the three terms (points, lines, and polygons) are relevant, specifically because the “real world” consists of points, lines, and polygons. Moreover, geodetic engineers represent the world through maps. This means that for every point, line, or polygon on the ground, there is a corresponding point, line, or polygon that can be projected on the map. However, one of the limitations of a map is that it cannot represent everything. It can provide detailed information of one place yet sacrifice the coverage that it can represent. It can also project a whole continent but the details are limited. This is because a map is only an abstraction of reality. It can’t give you all the information about everything.
What is the difference between topology and topography?
In Euclidean geometry, topology deals with the properties of a figure are constant even if it is distorted. In geodatabases, this defines and enforces data integrity rules like the polygons should not have any gaps between them (ESRI GIS dictionary). Topography, on the other hand, is the study of mapping of land structures, including relief, relative positions and elevations, and the position of natural and constructed features (ESRI GIS dictionary).
What is an ellipsoid? List the common ones used in Canada.
An ellipsoid is a closed geometric shape in 3D in which all planar sections are elllipses or circles (ESRI GIS dictionary). That is all the cross-sections of this surface are ellipses. It has three independent axes and it becomes an oblate ellipsoid of revolution when it is used to represent the earth. This is by rotating an ellipse about its minor axis.
The most commonly used in Canada are the two datums: the North American Datum of 1927 (NAD27), and the North American Datum of 1983 (NAD83). The former uses the Clarke ellipsoid of 1866. The latter uses the Geodetic Reference System of 1980 (GRS80), a newly established ellipsoid (Canada Government). They both are recognized geographic reference systems in Canada. They have different origin and measurements, either of the two can be used depending on the the province or place in Canada.
What type of data is the Raster Model best suited to represent? Give examples.
Raster Data Model is a representation of the world as a surface divided into a regular grid of cells (ESRI GIS dictionary). This is best suited for storing data that varies continuously like a satellite image, an elevation surface, or an aerial photograph. Anything with a continuous surface can be suited for the raster data model.
Explain the differences between NAD27 and NAD83?
The NAD27 or the North American Datum of 1927, and the NAD83 or the North American Datum of 1983 are both geodetic reference systems. However, they vary on the measurements and the reference ellipsoids that they use (Canada Government). NAD27 uses the Clarke Ellipsoid of 1866, while the NAD83 uses the Geodetic Reference System of 1980. The former has its reference fixed point in Kansas, while the latter has the center of the earth.
When converting the coordinates between NAD27 and NAD83, the Geodetic Survey of Canada developed the National Transformation software capable of doing so. And because different provinces in Canada uses different reference systems, transformation of the coordinates from NAD27 to NAD83 coordinates, or vise-versa, is important (Mugnier). Also, one of the reasons why the NAD83 was developed using the new Geodetic Reference System of 1980, was that when Canadian surveyors observed more lands to cover the whole country, it produced hundreds of baselines, additional points with astronomic coordinates and azimuths, and they are all accurate with the use of their equipment. The problem was, Clarke Ellipsoid of 1866 did not fit anymore with the modern geodetic network that was developing. That is why the GRS 1980 was the used for the new geographic reference system. Although this might be the case, the NAD27 still serve a purpose for it is the original datum. Some coordinates may need the NAD27 coordinates, some might need the NAD83 coordinates.
Describe the UTM system. Use a diagram to help with the description. Diagram should show the Central Meridian with its False Easting value, origin for both Northern and Southern hemispheres with their values, and extents of zone for both east/west and north/south.
The UTM system or the Universal Transverse Mercator system is a special grid that was developed for military used by the National Imagery and Mapping Agency, formerly known as Defense Mapping Agency, throughout the world (USGS). This divides the world into 60 zones from North-South with 6˚ wide of longitude (Lampinen). These zones are numbered from Zone 1 to 60. Zone 1 is between 180˚ and 174˚ West longitude while Zone 60 is between 174˚ and 180˚ East longitude.
A central meridian can be drawn through the middle of each 6˚ zone with a false easting value of 500,000 meters (USGS). This is to provide grid values of less than 500,000 if it belongs to the left of this meridian, while it is more than 500,000 if it is on the right of the meridian. The reason behind this is that the 6˚-wide longitude is about 667,000 meters maximum, which means that whether you are in the left or right of the central meridian for that zone, it can never be lower than 166,000 meters or greater than 834,000 meters (Dutch).
The origin of latitude is the equator (Lampinen). False northing is assigned 0 at the equator for the Northern Hemisphere and 10,000,000 meters at the equator for the Southern Hemisphere. The latitude values span from 80˚ South to 84˚ North. The scale factor at the Central Meridian is 0.9996 (Lampinen).
The figure below is the UTM of the whole world.
Norway and Svalbard are exceptions from the 6˚-wide zones (Morton). The latitudes are lettered from C through X, not including I and O. All of these bands are 8˚ wide except for band X which is 12˚ wide (Lampinen).
References:
Canadian GIS Data Sources. (2015). Retrieved February 14, 2016, from http://canadiangis.com/data.php
Canada Government. (2015, Nov. 27). Datum. Retrieved February 14, 2016, from https://www12.statcan.gc.ca/census-recensement/2011/ref/dict/geo017-eng.cfm
DMAP: UTM Grid Zones of the World. (n.d.). Compile by Alan Morton. Retrieved February 14, 2016, from http://www.dmap.co.uk/utmworld.htm
Dutch, S. (2014, Apr. 10). The Universal Transverse Mercator System. Retrieved February 14, 2016, from https://www.uwgb.edu/dutchs/FieldMethods/UTMSystem.htm
Free Data - GeoGratis. (n.d.). Retrieved February 14, 2016, from https://www.nrcan.gc.ca/earth-sciences/geography/topographic-information/free-data-geogratis/11042
GeoBase portal transitioning to GeoGratis / Transition du portail GéoBase vers GéoGratis. (n.d.). Retrieved February 14, 2016, from http://www.geobase.ca/
LUOMUS. (n.d.). Retrieved February 14, 2016, from http://www.luomus.fi/en/utm-mgrs-atlas-florae-europaeae
Mugnier, C. J. (1997 Dec.). Grids and Datum: Canada. Retrieved February 14, 2016, from http://www.asprs.org/a/resources/grids/12-97-canada.pdf
Open Data. (n.d.). Retrieved February 14, 2016, from http://open.canada.ca/en/open-data
Support. (n.d.). Retrieved February 14, 2016, from http://support.esri.com/en/knowledgebase/GISDictionary
The Atlas of Canada. (n.d.). Retrieved February 14, 2016, from http://www.nrcan.gc.ca/earth-sciences/geography/atlas-canada/
The National Soil DataBase (NSDB). (n.d.). Retrieved February 14, 2016, from http://sis.agr.gc.ca/cansis/nsdb/index.html Esri Canada. (n.d.). Retrieved February 14, 2016, from http://www.esri.ca/en
USGS. (2001, Aug.). The Universal Transverse Mercator (UTM) Grid. USGS Fact Sheet 077-01. Retrieved February 14, 2016, from http://pubs.usgs.gov/fs/2001/0077/report.pdf
