DEM-TIN definitions
23 FebElevation: Elevation is the height of a geographic location above a reference point, most commonly a reference geoid. http://en.wikipedia.org/wiki/Elevation
Slope: The slope of a line describes its steepness. A Higher slope value indicates a steeper incline. Slope is defined as the ratio of rise over run. http://en.wikipedia.org/wiki/Slope
Z-values: The value for a given surface location that represents an attribute other than position. http://en.mimi.hu/gis/z-value.html
Triangulation: Triangulation is the process determining the location of a point by measuring angles to it from points at either end of a fixed baseline. The point can then be fixed as the third point of a triangle with one known side and two known angles. http://en.wikipedia.org/wiki/Triangulation
Resolution: Resolution can be defined as the amount of information shown on a screen, whether it is digital pixels or analog lines. The more lines or pixels the image possesses, the greater the image quality. http://www.tech-faq.com/screen-resolution.html
Zone: An area or a region distinguished from adjacent parts by a distinctive feature or characteristic. http://www.thefreedictionary.com/Zone
Raster: A method of storing, representing or displaying spatial data in digital form. Consists of using cell data arranged in a regular grid pattern in which each unit within the grid is assigned an identifying value based on its characteristics. http://geoapp2.gov.mb.ca/website/MAFRI/Glossary3.html
Contiguous data: Contiguous data is data that is moved or stored in a solid uninterrupted block. Contiguous data can be accessed more quickly than data that is stored in fragments because fewer operations will be required. http://searchsqlserver.techtarget.com/definition/contiguous
Mass points: An irregularly distributed sample point, with an x-, y-, and z-value, used to build a TIN. Mass points are chosen to capture the more important variations in the shape of the surface being modeled. http://en.mimi.hu/gis/mass_point.html
TIN: The TIN model represents a surface as a set of contiguous, non-overlapping triangles. Within each triangle the surface is represented by a plane. The triangles are made from a set of points called mass points. http://www.ian-ko.com/resources/triangulated_irregular_network.htm
File types
21 Feb.dwg: (drawing) is a binary file format used for storing two or three dimensional design data and metadata. Developed by Autodesk, Open Design Alliance and others. Type of format: CAD
.dxf: AutoCAD DXF (Drawing Interchange Format, or Drawing Exchange Format) is a CAD data file format for enabling data interoperability between AutoCAD and other programs. Developed by Autodesk. Type of format: CAD data exchange.
.dwf: Desing Web Format (DWF) is a secure file format for the efficient distribution and communication of rich desing data to anyone who needs to view, review, or print desing files. Developed by Autodesk. Type of format: CAD
.dgn: (Design) is the name used for CAD file formats supported by Bentlry Systems’ MicroStation and Intergraph’s Interactive Graphics Desing System (IGDS) CAD programs.
.txt: A text file is a kind of computer file that is structures as a sequence of lines. Text file refers to a type of container, while plain text refers to a type of content. Text files can contain plain text, but they are not limited to such.
.asc: Files with an extension of “ASC” are usually ASCII text files which offer basic word development functionality, similar to the .txt file format. ASC files can be viewed and edited using a text editor For Windows, while double-clicking an “ASC” file does not normally open Notepad, these files can normally be viewed with such a tool.
.xml: Extensible Markup Language (CML) is a set of rules for encoding documents in machine-readable form. Developed by World Wide Web Consortium. Type of format: Markup language
.gml: Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. Type of format: Geographic Information System.
.kml: Keyhole Markup Language (KML) is an XML schema for expressing geographic annotation and visualization within internet-based, two-dimensional maps and three-dimensional Earth browsers. Developed by Keyhole, Inc. and Google. Type of format: Geographic Information System.
.kmz Keyhole Markup Language files when compressed.
Generalisation questions
16 FebWhy is generalization necessary?
Generalization is necessary because it reduces cost and simplifies detail for ease of comprehension.
How is it related to map scale?
As the scale decreases the ammount of detail shown is reduced.
What happens to point, line and area features as scale decreases?
Details are simplified, smaller details begin to dissapear as you reduce your scale. Dimensionality may eventually collapse.
What is the difference between selection and simplication?
In simplification, as scale goes down features eventually will lose dimensionality. Selection dictates which elements will remain, details vary depending on scale
What are the three types of data catagorisation (classification)?
Nominal, interval and ordinal
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