Introduction To Gis

An introduction to Geographic Information Systems (GIS) Introduction: the 5 pillars upon which the electrical power distribution systems automation is built are: computer programming, computer aided design & drafting (CADD) including drawing digitization, system control & data acquisition (SCADA) systems, local networks including LAN & WAN, geographic information systems (GIS) including global positioning system (GPS) software. In this article an introduction to GIS, just the tip of the iceberg, will be presented. GIS is a computer tool that allows the user to position, analyze and verify objects & events of geographic nature and produce an output in a geographic form (maps & tables). It is a software that links information about where things are with information about what things are like. The components that build the (digital) maps are distributed on different layers. The user enter different geographic features on different layers (this characteristic is similar to CAD software packages). When the user retrieves the map, to be displayed in front of him/her on the screen, he/she decides which layers to be shown based on the information required. Thus certain layers (information) can be suppressed if they are irrelevant to the task at hand. A digital map created by GIS will have points (dots) that represent features on a map like cities, polygons (small areas) that represent features such as lakes and arc (lines) that represent features like roads. The GIS software can be considered a package made up of sub packages that can communicate and understand each other. It can access data directly from other software packages like geographic data & shapes, CAD drawings, databases, images or can import & export data from/to other programs. These integrated characteristics provide the full functionality of a GIS which includes: statistical analysis & research (similar to commonly used database software packages), entering, storing, manipulation & analysis of data in geographic style (functionality for a mapping or geographic information system) and displaying output results or producing of documents for presentation purposes in tables and/or map forms. The output results are laid out in geographic format that provides a much clearer and easy to understand presentation. These features of the GIS distinguishes it from other information technology systems and makes it a tool of great value to public as well as private users when it comes to presenting well explained, informative documents, to providing the required results of an analysis and showing the assumptions upon which the results are based, to forecasting the outcome based on the available factors & variables or in preparing strategic plans. The preparation of maps and reports based on geographic analysis are not new activities, but with the GIS the outcome is produced faster, consistent & accurate. Before, only few persons had the knowledge and were able to access these geographic data (examples for such data needed with the GIS are given later in this article) in order to make decisions or solve problems. Now, the GISs are taught in secondary schools and post secondary institutes world wide. The industry is in the millions of dollars and employs hundreds of thousands workers. Components of a GIS: there are 5 main components that build a GIS, they are: hardware, software, data, users & methods. The hardware: it is the computer upon which the GIS runs. Now, the GIS software run on a wide scope of hardware platforms, from server to desktop as stand alone or in a network. The software: it provides the functionality and the tools for entering, storing, analyzing and presenting the geographic data/information. The key components of the software are: the appropriate interface to enter and manipulate the geographic data, database management system,

tolls for the analysis & search of information and displaying output results, an easy graphical user interface to all the capabilities available from the software. Data: the most important part of a GIS is the data. The geographic data & the alphanumeric information with their relevant data can be obtained from other users or purchased from a third party (data supplier). A GIS is able to integrate spatial (information about the location & shape of and relationships among geographic features usually stored as topology & coordinates) & geographic (the locations & descriptions of geographic features, usually they are spatial & descriptive data - describing the characteristics of geographic features) data with other sources of data and it can use commonly used database management system as a major part of its structure to organize & maintain the latter data and even to manage the spatial data themselves. Users: the system would have limited value without its users that manage the system and develop projects to solve real life problems. The users of GIS varies from technical specialists who design & manage the system to those who use the system to accomplish their daily work. Methods: a GISs have to produce well designed projects that are compatible with the specifications/regulations of the organization. They have to be flexible enough to meet the methods and procedures of each of the different organizations that will be using such systems. How does a GIS work? The system stores the geographic features (information) among different layers. Such features will be displayed on the screen as geometric shapes, points, lines or areas. For example a layer may have points that represent the cities in a region (or all the wells in an area), another layer of lines may represent all the streets in an area ( or watercourse in a region), a layer of areas can represent construction areas or similar use areas in a region. Each of the geographic features will have its own set of attributes (characteristics of such feature) that are described by numbers, characters, images and CAD drawings (typically stored in tabular format and linked to the feature by a user defined identifier). For instance a well might include depth and gallons per minute as its descriptive element. Each geographic feature will also have its exact geographic position expressed as coordinates, eg. Cartesian - planar (x,y), 3-dimension (x, y,z), vector, which is stored with its attributes. Though the system is built on simple idea but it is powerful & versatile. It solves a lot of real life problems from setting the route of a delivery truck, to deciding on the best way for emergency convoys to take, to storing all the important details of a municipality or a city like the location of Police & Fire stations, hospitals, parks, overhead & underground distribution systems, electrical service entrance points, meters locations, water pipes routes, sewage & storm sewage paths & locations, telephone lines, electrical power stations location & details, telephone end offices (local central offices), toll offices (tandem offices) & intermediate switching offices, environmental data and weather patterns. Geographical references: it contains an explicit spatial reference (those giving the latitude & longitude or a national coordinate system) or an implicit one like the address, postal code, a section from the census or street name. Thanks to an automatic process named geocoding (the process of identifying the coordinate of a location given its address) where explicit geographic reference can be obtained from implicit one, thus objects & events can be located on the Earth surface. Data structure models: the GIS works with 2 distinct types of data structures: vector & raster. In the former, the information about points, lines & polygons are codified & stored like a collection of x,y coordinates. For a point feature, it is presented by a single x,y coordinate, a line feature (a

street or river) is presented by a series (string) of x,y coordinates, a polygon feature like sales areas or a hydraulic reservoir are stored as perimeters of a homogeneous area. This model sets itself well for describing discrete phenomena and events. For continuous events or properties like elevation, slope, temperature or precipitation that varies continuously in space, the raster dats structure is applied. The raster is a cellular data structure composed of rows and columns for storing images. Groups of cells with the same value represent features. Another geographic data model representing information as an array of equally sized square cells arranged in rows & columns is known as grid. Each grid cell is referenced by its geographic x,y location. The grid cell is a discretely uniform unit that represents portion of the Earth. Each grid cell has a value that corresponds to the feature or characteristic at that site. The geoprocessing system based on this model (cell-based) allows sophisticated spatial modeling & analysis. Spatial analysis & modeling: spatial analysis is the process of modeling, examining and interpreting model results. It is useful for evaluating suitability & capability, for estimating & predicting and for interpreting & understanding. Traditionally there are 4 types of spatial analysis: topological overlay & contiguity analysis, surface analysis, linear analysis and raster analysis. Spatial modeling is the analytical procedure applied with a GIS. There are 3 categories of spatial modeling functions that can be applied to geographic features within a GIS. They are: geometric models, coincidence models & adjacency models. All of which support operations on spatial data such as points, lines, polygons, tins (triangulated irregular network) & grids. Tasks of a GIS: the general objective of a GIS is to essentially fulfill the following 5 tasks: data entering & saving, data manipulation, management of system, research & analysis on the data entered & acquired and displaying & viewing the sought information. Entering & saving data: before starting to use the GIS, the data has to be converted into a suitable digital format. The action of converting of the data on paper map into equivalent electronic files is called digitizing. For small projects the data are converted (entered) manually using a digitizer, for large projects a scanner is used to convert the data into electronic ones. A digitizer is a device that consists of a table & a cursor with crosshairs and keys to digitize geographic features (similar device was used when engineering drawing was digitized and entered into a CAD system). The process of using a digitizer to encode the locations of geographic features by converting their map positions to a series of x,y coordinates stored in computer files. Pushing a digitizer button records an x,y coordinate. A digitized line is created by recording a series of x,y coordinates. Scanner is a device that, automatically, captures data (from hard copy) in raster format and saves it to an electronic file. Some scanners use software to convert the raster data to vector one. Data manipulation: it will be most likely that the data required for a GIS project would have to be transformed or manipulated to render it compatible with the system at hand. One example would the availability of information at different scale than the required by the project. Before such data can be integrated and used, it has to be brought to the same scale as in use for the project. Such transformation of data can be of temporary nature for viewing purpose only or permanent to be saved to the disk to perform an analysis later on such data. The GIS provides a lot of tools to manipulate spatial data and to eliminate non essential data. Data & information management: for small GIS projects it would be sufficient to save the geographic information as simple electronic files. Obviously, when the amount of data increases as well as the number of users, a DBMS (data base management system) is used to allow saving,

organizing and managing the data. A DBMS is nothing more than another software used to manage data bases. Practically, there are 3 distinct models of a DBMS. They are the hierarchical, the network & the relational models. The first 2 are quite complex in the sense that they rely on the use of permanent internal pointers to relate records to each other. The process of inserting (entering), updating & deleting records using these types of databases requires synchronization of the pointers (a task that must be performed by the application). Relational databases rely on the actual attribute values as opposed to internal pointers to link records. Using a common attribute from each record, the linking of records is achieved. The GIS uses the relational model when it comes to data management. A RDBMS stores data like a collection of tables. As mentioned, common fields in different tables allow linking the tables together. Because of its simplicity & flexibility, RDBMS found a wide use in the different applications including the GIS. Research & analysis: a GIS can answer for example any of the following questions: What is the distance between 2 places? Which are the industrial parks in the region? Who is the owner of a certain property? Which sites are the most suitable for building high rise apartment building or a lodge for the elderly? What is the type of soil prevalent in certain area? What would be the consequences of building a free way in a certain stretch on the flow of traffic? It can be seen from what is mentioned previously that the GIS allows performing simple research as well as sophisticated ones for the purpose of presenting timely information to the analysts & managers. The GIS technology demonstrates all its capabilities when it is used to create models (simulating a real problem using specific data with existing or new systems), spotting trends & singling out specific events and when the "what if" scenario for different options is to be researched. The different types of analysis that are performed using a GIS can be classified broadly into: mapping where things are, mapping quantities, mapping densities, finding what's inside, finding what's nearby, mapping change and overlaying. Mapping where things are: allows the user to find places that have the features he/she is looking for and to see where to take action. Also, the GIS system is used to allow the user to find patterns by looking at the distribution of features on the map instead of just individual feature. Mapping quantities: users map quantities such as where the most & the least are, to find features that meet their criteria or to see relationships between features. Mapping densities: it lets the user measure the number of features (per unit area for example) using a uniform area unit, so the distribution is observed. Finding what's inside: such systems are used to monitor what is happening inside a specific area, and take the appropriate action based on such observation. Finding what's nearby: the user can find out what is occurring within a set distance (a buffer) of feature using this analysis type. Mapping change: the user can map a change of a feature or characteristic for a specific area, in order to anticipate the future condition regarding such variable, to decide on a course of action or to evaluate the result of a policy or an action. Topological overlay: it is an analysis procedure for determining the spatial coincidence of geographic features. This analysis can also be applied between feature classes. Identity is the topological overlay of a coverage (input) with a polygon coverage (identity). For each feature in the input coverage, the intersection with identity features is determined, creating new features of the same feature class as the input coverage. Intersect is the topological integration of spatial

data sets that preserves features that fall within the area common to both input data sets. Relational join is the operation of relating and physically merging 2 attribute tables (a tabular file containing rows & columns, such tables are associated with a class of geographic features eg. roads, wells,..etc., each row represents a geographic feature & each column represents 1 attribute of the feature) using their common item. Displaying & viewing: the output of GIS will most probably be displayed geographically or graphically. Providing maps to explain and clarify geographical and geographically- related topics is the most effective method of presenting & communicating such information. The GIS is providing new tools for extending the art & science of cartography. The production of such maps can include for example reports, 3-D drawings, photos and other multimedia products. Data for the GIS: examples for data that are used with these systems are: basic maps (including roads & freeways, rivers & lakes, parks & amusement sites, administrative & postal zones), Organizations map (demographic, consumer products, financial services, real estate, health, telecommunication, companies, transportation and emergency), environmental maps (weather patterns, hazards, satellite images, natural resources & topography) and general reference maps (all the data that will build the user own fundamental database, national & international maps & data). Selecting the right data: answering a few questions will allow the user to decide upon and find the required data for modeling and the analysis needed. These questions are: What does the user want to do with the data? (an obvious question), What are the specific geographic features needed for the application? What attributes of such feature are required? What is the geographic extent of the area of interest? What is the type of data & level of geography that have to be examined within the area of interest? How current must the data be? What computing environment will be used for the modeling & analysis processes? Which GIS software will be used for the subject application? How many concurrent users will be accessing the data and at how many locations?