Primary and secondary data
Why is map design an important consideration when creating maps using a GIS? Every GIS map is created to serve a theme or more. Map elements are arranged in a map to make visualization of complex facts simpler. Principles of map projections, map scale, map generalization, map accuracy, symbolization and map composition guide the map maker to create map as per user needs in a cost effective and timely fashion. By map designing process, the map maker determines the required map elements to be included in the map to accurately convey the purpose in a pleasing manner.
Hence map design is an important consideration when creating maps using a GIS. (<www. esri. com/industries/k-12/download/docs/intrcart. pdf>) 2. What are the main elements of a map? Main map elements can be broken down into following broad areas: a) Primary elements: Primary elements set the right perspective of the map. These are map scale which is shown in map in verbal, numeric, or graphic form, direction indicated by a north arrow, legend lists the symbols used in map and explain what they represent and source of facts and figures given the map for their authenticity.
b) Theme related elements: They are directly related to the theme of the information being displayed in the map. Title which tells the theme of the map in exact words and size, projection tells which property (area, distance, direction, and shape) of earth feature is maintained at the cost of the other attributable to the theme of the map, and credits presenting the information about the cartographer of the map. c) Selective and effective communicable elements: As per the requirement of the map to improve its readability, map subset elements like neatness, locator maps, insets and index maps are used.
(<http://www. colorado. edu/geography/gcraft/notes/cartocom/elements. html>) 3. What mechanisms are available for the delivery of GIS output? GIS outputs are of two types; maps and non-cartographic outputs like charts and reports. These are delivered as hard copy GIS products and soft copy outputs over computer monitors and projectors. Due to technological advancements, internet is the preferred choice of delivery mechanism for diffusion of GIS products. 4. Describe how the use of the Internet has changed GIS output. Use of internet has brought a paradigm shift in the GIS output.
Nowadays internet users can access and query GIS maps without owing any GIS software and only by having web browser (Weise). Online updating of spatial and non-spatial databases brought dynamism to what was known as static maps. For example online traffic updates, weather updates, location based services, city navigation services, internet yellow pages are very popular services enabled by internet GIS. Thus use of geographic information has increased due to ease of communication through internet as a medium. 5. Describe the main phases of the data stream. There are two main phases of the data streaming of digital data.
Firstly, continuous data are broken down into data-packets with collective symbol code for each packet and transmitted. This is called Out-phase of data stream. At the receiver end, these data-packets are identified using collective symbols and grouped. This is called In-phase of data stream. For example, traffic speed data feed are streamed into the GIS system for real-time information on traffic. 6. What are the main data sources for GIS? The following are the main data source or inputs for GIS database: a) Paper or analogue maps which are transformed into GIS inputs by digitization/scanning techniques (Base maps).
b) Tabulated data attributed to spatial data (Attribute data). c) GPS location inputs as spatial data for GIS (Vector data). d) Satellite imagery and aerial photographs (Raster data). (<http://www. gis. com/whatisgis/whatisgis. pdf>) 7. What are the main problems associated with using the web to find GIS data? The main problems associated with using the web to find GIS data are enumerated below: a) GIS data available in web are vendor specific and not open. This means, the data in its available format useable in one application may not be useable in other GIS application. b) Spatial data are very sensitive.
In many cases, authentication and authority of data available in web are difficult to ascertain. c) Handling high volume of spatial data through web browsers is time consuming task. d) Sophisticated technical support for complex GIS workflows are difficult to get over web. (Amirian P, Mansourian A) 8. What methods are available for detecting and rectifying errors in: • attribute data, and • Spatial data? Errors occur due to inadequate data acquisition methods which do not truthfully capture the real world phenomena. This concept is similar with statistical treatment of error in terms of bias and precision.
That is, encoded values represent approximations. So errors can be reduced through the use of more refined data acquisition techniques and methods of repeated sampling. Apart from this is the inherent variability of geographical phenomena. In case thematic attributes, methods for measuring and documenting error can be differentiated in terms of the scale of measurement as appropriate, whereas for interval and ratio data, error can be measured in terms of the mean deviation between actual and observed values at a sample of locations. This provides an error index analogous to the root mean squared error (RMSE) for elevation data.
9. What are re-projection, transformation and generalization? Re-projection Re-projection is a mathematical method of conversion of a map from defined or undefined coordinate system to another defined coordinate system. This is carried out to generate GIS of common projection maps. Transformation It is a spatial data conversion process. Transformation is the process of changing the map coordinates or a digital imagery from one system of coordinates to another, usually by shifting, rotating, scaling, skewing, or projecting them. Generalization It is the main process of map design.
As per the theme of the map, map features are abstracted, reduced, and simplified for change of scale or resolution. For example, in the generalization process of a vector map, density of points in a line is reduced keeping the line feature’s general shape. For optimization of raster map resolution, generalization is achieved by enlarging and resampling cells. (http://support. esri. com/index. cfm? fa=knowledgebase. gisDictionary. gateway) 10. What is geocoding? A GIS operation of giving geographic location (latitude/longitude reference) to street addresses of features in the street segment for adding as layer in GIS.
Positional accuracy of such coding can be optimized by creating the point feature on the centroids of the parcels. Ratcliffe, Jerry H. (2001). <http://jratcliffe. net/papers/Ratcliffe%20(2001)%20On%20the%20accuracy%20of%20TIGER-type%20geocoding. pdf>. 11. Suggest 10 applications for buffering (Answers should include point, line, and polygon examples). Answers should include what you are buffering, why you are doing it, what can you use the buffer for, and some approx. distances you may use. Buffering is a powerful GIS functionality used mainly in distance measurement related problems.
It finds application in various GIS problems as mentioned below: a) A multiple rings with specific distance (rings of approx 30 kms width) around a city (Point feature) can be buffered for business development project. This will help to locate site for new business development that satisfy the preset conditions. b) A water body like river (line feature) or dam (polygon feature) can be buffered with zones of flooding level to identify the areas prone to flood damage. c) Courier businesses may apply parcel charges as per distance. Buffers of 10 kilometers centered at the collection centre (point feature) can be generated.
By identifying the destination area in the buffer ring, charges applicable are calculated with rate multiplied by number of rings. d) Progressively less polluted zone can be identified by creating buffer polygons around a road segment using gravity model or distance decay model. e) New infrastructure like roads can be build avoiding encroachment in protected forest area by applying buffer zonation in wildlife sanctuaries. Buffer width (e. g. 5-10 kms) can be determined by taking into account human pollution factors. f) GIS can be used to delineate an effective riparian buffer (e.
g. 50-200 meters) to protect stream water quality. g) Buffer area (e. g. a zone of 5-10 kilometers) around historical monuments can be generated to protect it from setting up of hazardous industry and monitor air pollution on roads around it. h) Protective buffer zones around wildlife habitat can be identified using GIS to avoid human settlements in the forest area and disturbance to local eco-system. i) Disease spread zone can be buffered using infecting-vector data available with public health authorities to identify spatial relation and take remedial measures.
j) Satellite swath can be buffered (70 – 250 kms width) with their nadir positional data (line feature) and sensor parameters to identify areas for imaging. (Bruce Ellsworth Davis) (Said Easa, Yupo Chan) 12. With regards to data analysis, explain queries reclassification buffer intersection By the nature of GIS data, queries are broadly classified into two: Query on Attributes and Query on Geography Queries selectively retrieve information on existing database. Complex query involving selection based on both spatial as well attributes can be executed which are specified by context of data analysis being performed on the GIS.
The outputs of this query can be exported into a map layer and can be used for further data analysis. Reclassification Reclassification is a spatial analysis technique employed on raster data to select and replace input cell values with new output cell values. Reclassification helps to simplify or change the interpretation of raster data by changing a single value to a new value, or grouping ranges of values into single values—for example, assigning a value of 1 to cells that have values of 1 to 10, 2 to cells that range from 11 to 20, and so on. Buffer Buffer is a useful GIS function in data analysis.
Some important uses in various analysis are given below: a) A buffer is useful for proximity analysis. For example, ring buffers can identify all residential areas located within 5 kilometers from a school. b) A buffer polygon in spatial analysis, can enumerate the enclosed point, line, or polygon feature at a specified distance. Intersection Intersection is a type of vector overlay operation employed in spatial data analysis. Intersection considers common interest in both input layers but only within the bounding area to produce a resultant output layer.
For example intersection operation to find number of national highways falling within the forested area will result in a polygon with number of national highways bounded by the forest area. 13. What are the various options for vector overlays? Explain the methods and the outcome of each. The common options applied for vector overlays are: a) Clip This method uses the cookie cutter approach. Though the clipping layer defines the boundary of clipped layer, output layer does not retain the attribute of both input layers.
For example, clipping operation to know the hospitals falling within the municipal limits of a city layer results in a point layer of hospitals encompassed in municipal limits. b) Intersection Intersection overlay results in output layer which posses the spatial and non-spatial attribute data of both the input layer but within the bounding area. Features outside the bounding area are discarded. Here the order of intersection is important. If intersection query is run on the above example, a polygon layer of municipal limits encompassing hospitals within will result. c) Union
Union overlays combines both spatial data and bounding area layer to create a new output layer retaining the attributes of both input layers to the extent of the bounding area. If union operation is queried on the above example, the resultant polygon layer to the extent of the city with hospital features will be obtained. (<http://www. sowamed. ird. fr/resource/RES247_WP6_GISanalysis_AlBakri. pdf>) 14. Select one of the following applications and discuss how GIS could be a useful tool • a fire in underground transit system • the aftermath of an ice storm • real estate sales
• site selection for an elementary school You are free to make any assumptions you think are necessary. State briefly what the assumptions are. Site selection process for an elementary school requires careful study, including a thorough and objective evaluation. The school site must help positively to the health, safety and social aspects of a child’s life at school. These broad guidelines when studied in the light of their relation to the local situation should provide a basis for the objective selection of the best site available. GIS is very useful to focus and manage the site selection process.
In the present case the following criteria, which are listed in the general order of importance is evaluated. 1. Safety 2. Location 3. Environment 4. Soils 5. Topography 6. Size and Shape 7. Accessibility 8. Public Services 9. Utilities 10. Cost 11. Availability For multi criteria evaluation, a fuzzy logic system like MATLAB tools can be used to generate a numerical output which indicates relative suitableness of the parcel in a given area. GIS can be used to exploit the evaluation results and achieve a result regarding the suitable places for school site.
First the map with 1:25000 scale of the area has to be topologically structured using Arc/Info software, and then the file exported to Arc View as a map layer. By adding all the required parameter maps as layers, a spatial database is constructed. Then a spatial query based on the multi-criteria evaluation output will result in selection of the most suitable, suitable and unsuitable parcels for School site. Assumptions: The following factors are assumed which are implicit requirements for the success of the project: 1. It is assumed that a large track of land is available for evaluation.
Primary and secondary data are readily available with common projection coordinate system. 3. Weightage for each criterion is given by interested parties like school administration, parents, environmentalist, town planning authority and area administration. Works Cited www. esri. com. 19 May 2009. <www. esri. com/industries/k-12/download/docs/intrcart. pdf> www. colorado. edu. 19 May 2009. <http://www. colorado. edu/geography/gcraft/notes/cartocom/elements. html> www. gis. com. 19 May 2009. <http://www. gis. com/whatisgis/whatisgis. pdf> Amirian P, Mansourian A. Developing a GIS Web-Service using . NET Technologies, New Delhi: Mapindia, 2006.
Ratcliffe, Jerry H. On the accuracy of TIGER-type geocoded address data in relation to cadastral and census area units. International Journal of Geographic Information Sciences 15 (5), 2001 www. support. esri. com. 19 May 2009. <http://support. esri. com/index. cfm? fa=knowledgebase. gisDictionary. gateway> Bruce Ellsworth Davis. GIS: a visual approach Page 261 edition: 2, Cangage Learning 2001 Said Easa, Yupo Chan. Urban planning and development applications of GIS page 283, Geographic Information System committee 1999. www. sowamed. ird. fr. 19 May 2009. <http://www. sowamed. ird. fr/resource/RES247_WP6_GISanalysis_AlBakri. pdf>Sample Essay of RushEssay.com