Archive for February, 2011

dem questiond pt 2

4a there is no slope, the ground is a flat surace at that elevation
4b the elevation drops i think

bc hydro sucks

What are the differences? the 5m contours are way more detailed and the further apart the contours get it gets less detailed
Were the results what you expected? yes
What are the 2 highest elevation points on the PG_Cont5_TIN? 885 and 880

1. TIN-(Triangulated Irregular Network) A vector-based data structure for storing terrain information in digital terrain modeling, it is a surface representation derived from irregularly spaced points and breakline features. Each sample point has an x, y coordinate and a z value or surface value.

2. Interpolated values-interpolation is a method of constructing new data points within the range of a discrete set of known data points, the interpolated values can be represented by color or number etc.
3. Mass points-An irregularly distributed sample point, with an x-, y-, and z-value, used to build a triangulated irregular network(TIN). Ideally, mass points are chosen to capture the more important variations in the shape of the surface being modeled.

4. DEM-(data elevation model)-a DEM file is a simple, regularly spaced grid of elevation points .A DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a triangular irregular network (TIN). The TIN DEM dataset is also referred as a primary (measured) DEM, whereas the Raster DEM is referred as a secondary (computed) DEM

5. Contiguous data-Data that are stored in a collection of adjacent locations in a computer memory device,
contiguous data is data that is moved or stored in a solid uninterrupted block. In general, contiguous data can be accessed more quickly than data that is stored in fragments because fewer access operations will be required. Files are sometimes stored in fragments so that storage space can be used more efficiently (all the small spaces can be used).

6. Re-sampling-can refer to re sizing of images or data sources it can also be a filter to the data and changes the sampling rate of the signal by decimation or interpolation.

7. Raster- Raster data is a grid of cells covering an area of interest. Each pixel, the smallest unit of information in the grid, displays a unique attribute.An example of raster data is a scanned image or photograph. A line drawn in a raster format must be defined by a group of pixels along the length of the line. As a result the size of a raster file is larger than that required by a vector file.

8. Cell-is a three-dimensional polyhedron element that is part of the boundary of a higher-dimensional polytope

9. Zone-a zone is an area of set perametres that has information inside of the certain area
for example pg is in utm zone 10, a specific area that has been divided out of the bc zones.

10. Grid-can be used to define locations on maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to features.
for example x,3 y,7

information from: › GIS

File types

.DWG(drawing)- a file type used for storing two and three dimensional formats, it is used in such programs as INTELLICAD and AUTOCAD

.DXF(Digital exchange format)-File type used as an exact representation of the data in the AutoCAD native file format, the .dxf file has become less useful since AutoCAD has become more powerful.

.DWF(digital web format)-dwf is a secure file format developed byAutodesk for the efficient distribution and communication of rich design data to anyone who needs to view, review, or print design files.

.DGN(Design) This is the file type for CAD file formats which can be supported by microstation, the dgn format has two versions.

.CSV(comma seperarted values)-A file format which is used to store tabular data

.TXT(text)-A file format that is structured for a series of lines containing characters.

.XML(extensible markup lanugage)- a set of rules in machine readable forms which is encoded into documents

.GML(Geography markup language)-is the XML grammar defined by the open geospatial consortium to express geographical features.

.KML(keyhole markup language)- is an XML schema for expressing geographic annotation and visualization within internet based, two-dimensional maps and three-dimensional earth browsers.

.KMZ(Keyhole markup-zipped) A kmz file is a zipped keyhole markup language used to decrease the size of data.

Info source-

my map


1. Generalization is neccesary because people can not process so many details at one time, if you have tiny tiny details on a map alot of it wont mean anything.

2.The larger the scale the more detailed the map can be but when a map is at a small scale then things have to be generalized in ways such as using points instead of a city polygon

3.As the scale decreases the features become less detailed and more of a generalization

4.simplifacation determines the most important characters and selection makes it have fewer features and details.

5.The three types of data categorisation are nominal,ordinal and interval

Quantum GIS

          Quantum GIS is a user friendly GIS software, it runs on Linux, Unix, Mac OSX, and Windows and supports numerous vector, raster, and database formats and functionalities.QGIS has alot of features similar to ARC such as identify/select features,feature labeling, scale bar/north arrow etc. Also in QGIS you can view and overlay vector and raster data in different formats and projections without conversion to an internal or common format. This software was developed by Gary Sherman began in early 2002, For Mac users, the advantage of Quantum GIS over Grass GIS becauseit does not require the X11 windowing system in order to run, and all around the interface is much cleaner and faster. QGIS offers a selection of plug- ins to better increase the preformance of the free QGIS software, in reviews the QGIS user is satisfied with the product except for the lack of some tools but for a free program it is surprisingly versartile and has some good tools as well for example the editing tools make it simple and easy to create and edit projects.Quantum GIS is available free on their website.