Use of Geographical Information Systems - Essay Example

?Geographical Information System (GIS) The main components of GIS are hardware, software, methods, people and data. Data refers to raw geographic information which could be collected in house, compiled to custom specification or obtained them from a commercial data provider. Programs and an interface make up the GIS software component. Their functions include generating, analysing, manipulating, storing and displaying geographic information or data (Delaney and Niel 2006). Examples of these include IDRISI, Microstation, SPANS and AutoCAD Map. The hardware component of GIS is the central processing unit (CPU) or computer. It also includes a digitizer scanner whose function is to change data for example those found in maps into digital form then send the converted data to the CPU. There are also a tape device whose function is to store programs or data on magnetic tap, and a display device which is used to display data that has been processed. People as a component of GIS include end users and specialists whose function is to design the GIS for the end users. Methods refer to those procedures or techniques used data collection or processing. The functional elements of GIS are data manipulation, data input and output, data retrieval and display, data analysis and modelling and data management. Data input refers to incorporating data into the GIS whereas data output refers to removing data or information from the GIS. Data analysis and modelling involves obtaining an understanding of relationships in the data collected and developing a model of the spatial phenomena. Data retrieval entails taking out data from a stored format for use whereas data display is the showing off of the derived or primary data (Delaney and Niel 2006). In GIS, spatial data represent features that are location-specific or geographic in nature. They include cell location like column and raw, and coordinates like longitudes and latitudes. On the other hand, attribute data give a description of feature in a specific location and they can be in numbers or text strings. Unlike spatial data, attribute data can be measured in ratio, ordinal, interval and nominal ratios. According to Delaney and Niel (2006), topology creates an awareness of the surrounding for the GIS by developing a spatial data relationship. It links spatial and attribute data to give information on what surrounds a feature. When representing continuous and discrete geographic features, vector data structure uses points, polygons and lines whereas raster data structure make tessellation on the representation surface through a repeated use of a square cell or a pixel. However, raster data structures are better at representing a continuous surface. Vector data structure support typology better and are more accurate in representing geographic features compared to raster data structure. Generally, raster data structure requires has a lower processing power requirement compared to vector data structure. On-screen digitising, converting, importing and geo-locating/geo-rectification are the four common methods of incorporating digital data into a GIS. On-screen digitising involves locating features from digital sources for example satellite or scanned images using a computer mouse. Attribute data is entered through computer keyboard. Geo-locating is used to input non-geographic/non-georeferenced data into GIS because it converts spatial data into geographic data. Converting is done if GIS data is in a format that cannot be used by certain software. Importing involves obtaining data from other sources like geo-coded textual data, satellite images or digital aerial photographs into the GIS. There exist differences in cost, effort, time, and editing requirements between on-screen digitising, converting, importing and geo-locating/geo-rectification, scanning and vectorisation, table digitizing and keyboard entry as data input methods. Both importing and converting are fast, cheaper, need less efforts and have less editing requirements. Table digitising and keyboarding are slow, need more efforts and have medium editing requirements. However, table digitizing is expensive while the cost of keyboarding is low. On-screen digitizing and geo-locating have medium time and effort requirements and low cost. Their difference is that the editing requirements for on-screen digitising are medium and those of geo-locating are low. Scanning is slow and needs less effort but its editing requirements and cost are high (Delaney and Niel 2006). In GIS data input, accuracy and precision are important because they determine the level of correctness in terms of actual data location and level of details. During spatial data entry, the main errors encountered are vector and raster data entry errors. Vector entry errors may occur due to incorrect positioning of points or if there are incorrect nodes on the lines. They could also arise if the polygons contain duplicate lines, are incompletely closed or have dangles. Raster entry errors occur if comer referencing is done to the raster grids or if location shift occurs as a result of incorrect comer referencing. Data entry errors experienced when entering attribute data could arise from loss of attribute, lack of consistency in describing spatial features or incorrect data entry. Incorrect data entry could arise from incorrect attribute typing or incorrect data reading or observation. Loss of attribute could result from re-sampling of raster data or/and making a generalisation of vector data (Delaney and Niel 2006). In GIS, the detection and rectification of input data errors is critical because a small error which occurs at the beginning could become magnified during analysis leading to the presentation of invalid or incorrect results. This will in turn translate into incorrect or invalid modelling. Topology assists in the rectification of spatial data errors by automatically searching, noting and eliminating inappropriate duplicate lines and/or by finding and joining any nodes that are dangling within a radius. In real coordinate system, geographic information is mapped using existing actual coordinate values obtained from means of actual measurements like survey. These coordinates are based on a reference system or datum for example North American Datum (NAD) 1927 or NAD 83. In artificial coordinate system, geographic information is mapped without relating them to the real world because not all places or towns have tax maps registered to known coordinate system. In this case, the lowest corner is assigned a coordinate then coordinates of the other corners are calculated depending on their distances from point (0, 0). GIS data should be registered because it enables the ArcView to know the geo-referencing information to be included in the map. GIS data are projected because maps, for example topographical maps, reference to a small portion of the earth for example a country hence grid lines should be developed specifically for that purpose. Projection is also important in development of atlases of from globes which can then be used easily in the field. Projection helps to measure distances represented on a globe and compare the various regions represented (Delaney and Niel 2006). In Universal Transverse Mercator (UTM) projection, the various zones are standard and can be easily identified because the earth is sub-divided into 60 equal slices/stripes. It is developed from a grid made up of many projections put side by side. This makes it easy to designate an area as lying within a particular zone. A map is a representation of a three dimensional features as two dimensional/on a flat surface. Many of them are drawn to scale. When preparing a map, one should be concerned about the area being represented for example a town or a province because it will determine the scale to be used. One should also be concerned about the use of the map because it determines the details to be included and even major convectional colours and signs to be used. For example a map for town, district planning, forestry or mining. Map use will also determine the map title. During map preparation, a cartographer should be concerned about compass direction and it should therefore be indicated before proceeding with any drawing. The quality of the map output is a priority for GIS because it determines the visual clarity of the map and the understanding of its spatial context. This is important because GIS maps are increasingly being utilised globally by different people and departments to draw conclusions or make informed scientific decisions (Delaney and Niel 2006). A database refers to a system used for storing, organising and retrieving huge amounts of data/information. When the compilation of the information is finished, it can be kept and utilised from the database for a long time for example between 10-50 years. Therefore, they act as important stores of information. In GIS, a database is also utilised in abstracting very particular types of information concerning the reality and organise them in a useful way thus they act as a model of the world developed for particular applications. When creating a GIS database, it is important to maintain raster data in the highest resolution because each raster cell has a resolution which represents its cell size. Even those which do not exist have values hence each cell must be represented. Therefore, maintaining them at the highest resolution leads to representation of more details, reduces mixed pixel problem and reduces the amount of entry errors that occur. It is also difficult to change a cell from small to big size or the reverse. On the other hand, it is important to maintain vector data in its simplest form because they allow for more analysis especially for networks like rail, road and telecommunication networks. They are good in representing phenomena that is continuously changing for example rainfall patterns. A data dictionary refers to a centralised repository of information concerning the origin, meaning, format, usage and relationship of data to other data whereas metadata gives details of when and how the data was collected and by whom. Therefore, metadata gives a practical insight on a particular set of data. Control points refer to a group/set of points whose vertical and horizontal locations are known and are they found on both the GIS data layers and the digital image. Control points are used on the image. They are normally used when one wants to align an image to data or georeference maps that have been scanned into existing GIS data. Therefore, several of them are evenly distributed around the image. Since they are found on both the GIS data layers and the digital image, they are useful in finding a correspondence between a particular location in the image and the actual ground points. Control points that are identifiable on ground are useful when one wants to determine geometric properties and distances of the image. In order to select control points on the image, one needs thoroughly examine the digital image that is supposed to be georeferenced and make a comparison between it and the available GIS data. In the process of making examination and comparison, one ought to identify the points that appear both on the GIS data and are also evenly distributed on the image. These are selected as the control points. GIS is an information system because it integrates, edits, analyses, stores, displays and shares geographic information which can be utilised to make informed decision making. It also allows its users to make interactive queries, analyse the information and present the results obtained from various operations. An example is information on land use patterns. Once this information has been incorporated to the GIS database, anyone is free to analyse, display, retrieve and share the information. Different users are able to interact with this information for different purposes using different interactive queries. Over the past 30 years, GIS has experienced rapid growth and development, and expansion in its application as well as a result of continual advancements its software and hardware components. GIS uses advanced technology that allows for certain operations to be performed faster for example cartography. The tools used in GIS map development allow the user to have control how the data appears on the map being developed unlike manual cartography. Due to additional time dimension GIS produces up-to-date maps by merging old maps with satellite information. It produces better maps because of its additional effects like shading based on altitude which clearly portrays relationship between various map elements. Apart from being a store of information, GIS also allows the users to develop graphics which enable users to visualise and understand quickly the results of their analysis. This has made GIS more useful in decision making (Delaney and Niel 2006). GIS market is active leading to reduced prices and a resultant increase in its use. GIS has incorporated location-based services (LBS) hence expanding its areas of application. Hard copy data refers to data that are still found in a hard copy and have not been converted to a digital format. Examples include data in text, maps, images or other recordings materials. Digital data refers to data that exists as binary digits that are discrete and continuous. GPS data mainly include geographic information which can be easily integrated into the GIS. They represent actual objects for example roads or trees and exist in raster and vector types. Remote sensing data mainly exist as infrared, spectral data or roughness/heat. They are normally captured using sensors which have been removed from the real garget for example satellite and stored in raster format. The data collection methods use in GPS include static methods, rapid static method, continuous method, point positioning method, code differential method and kinematic/post-processing and real-time method. All these are basically survey methods. The continuous survey has a precision of 0.5 cm and it relies on continuously-operating stations or permanent Global Navigation Satellite System (GNSS) stations to obtain data. Rapid static survey has a precision of 1-3cm and data is collected at a minimum of 10 minutes per point. Kinematic surveys are local surveys which use mobile GNSS and have a precision of 1-5 cm. Code differential surveys rely on code data to get differential solution and has precision of 50-300cm. Data is collected for five minutes per point. Point positioning determines its coordinates using uses data from a single receiver. It has a precision of 100-300cm. In remote sensing, data collection involves the use of multispectral techniques using real-time sensing or recording devices. These methods are either passive or active. Passive methods detect natural radiation reflected or emitted by an object. They include infrared, charged-coupled devices, radiometers and photography. Active data collection for example radar involves emission of energy to scan areas and objects. Remote sensing data collection methods are able to obtain data from inaccessible or dangerous areas unlike GIS data collection methods. Reference Delaney Julie and Niel Kimberley (2006). Geographic Information System: An Introduction (2nd Ed). Oxford University Press. Oxford. Read More