Data Requirements of Geographical Information System - Coursework Example

A research into the data requirements of a Geographical Information System Part II, GIS Data Requirements s "GIS is a computer system designed for capturing, storing, integrating, analyzing and displaying data from a geographic perspective."1 The purpose of this paper is to conduct some research into the "Data Requirements of a Geographical Information System ". We will try to show an "outline of the Data Requirements of a GIS, Identify sources from which data can be obtained, and identify associated costs. Then we will Comment on the likely accuracy of the data and any limitations in the system."2 Part II, GIS Data Requirements The data in GIS or Geographical Information System, is referenced to Geography. These dada are organized into a set of layers of information, for example, Transportation, Land use, etc. These data sets, have the information that can be represented as"  Raw measurements (such as satellite imagery)  Compiled and interpreted information  Data derived using Geo-Processing operations for analysis and modeling Many of the spatial relationships between layers can be easily derived through their common geographic location. GIS manages data layers as specific objects and uses a wide collection of tools to work with the data layers to derive key relationships."3 The required data in the system can be of different types such as Vector, Raster, Grid, Attributes and Databases. Vector data can be presented as "Points" on the surface of a page that has x-y coordinate pair or "Lines" that connect two data points or "Polygons" to surround an area that infinite data points are concentrated in. Raster data is presented as matrix with Rows and Columns. They present data as pixels. They can present data as Cell-Based data or Image-Based data. Grid data, surround the calculation are by polygons and make the calculations much faster. Databases keep all the necessary information for GIS and because of this, they are considered as the most important foundation of such systems. Other data related requirements for a GIS are Shape-files and Geo-Databases." A Shape-file is a type of GIS data layer that is used to transfer vector data. Each Shape-file can contain only one feature class."4 "Geo-databases are object-oriented data models that are stored in a relational database management system. They enable you to store multiple feature classes and the topological relationship among them. All feature classes in a feature data set must share the same spatial reference. Geo-databases have the ability to implement sophisticated business logic that can build relationships between data types, validates data, and controls access (import, editing, & export). "5 The number of data types for Geographical Information Systems is vast and this causes an enormous number of sources get involved in the system but the number of sources is different from project to project. Number of sources are often used by the people in GIS are the information issued by Government Agencies and/or commercial businesses. Sometimes maybe the scope of a project would is different to these known sources but most of the times many valuable info could be learned from such sources. A few years ago, most GIS data were presented on papers instead of their digital forms in computers but at present time, vast amount of GID data is touch in a digital form. Digital data helps GIS experts to speed up their work and develop the GIS much faster. GIS data presentation in digital form can help developer to search and re-use datas much easier. In order to re-use GIS data, GIS experts must contact the owner or producer of data and work with them to get the access to a usable data. Another helpful way of obtaining GIS data is to search the World Wide Web and internet for distributed and shared data that is previously placed on web sites for public access. There are quite a lot of agencies related to Government or Major Business Industries that provide huge GIS data and they gain the access to use them to public with no or a very limited price." Bureau of the Census, United State Geological Survey, Soil Conservation Service, NASA, and Federal Emergency Management Agency, provide standard sorts of information for the entire nation. " 6 One important issue that needs attention is that the way data is stored in a Geographical Information System is different from the paper maps. Data accuracy is one of the issues that is different in GIS and maps. "Data accuracy is a statement of how closely a bit of data represents the real world. It applies to geographical information in all these ways: Data accuracy is a statement of how closely a bit of data represents the real world. It applies to geographical information in all these ways: What features have been omitted? What non-existent features are represented? How correct is their classification? How current is the data? How far away is a map feature from its actual location in the world? Last one, or Location accuracy is of interest here, and is generally stated in terms of uncertainty. Location accuracy includes: Absolute accuracy: How close is the location on the map or data representation to its real location on the earth? For example, 95% of the well locations are within 50 meters of their surveyed locations. Relative accuracy: How similar is a shape on the map or data representation to the shape of the object on the earth. For example, cut block boundaries do not vary by more than 10 meters from their actual shape. These are separated because a map object may have a very accurate shape, but not be registered (located) correctly. A rigorous statement of accuracy will include statistical measures of uncertainty and variation, as well as how and when the information was collected. Spatial data accuracy is independent of map scale and display scale, and should be stated in ground measurement units."7 Data accuracy is not the only fact. There are more things to be considered and one of them is "data precision". Data precision implicates to minor differences that exist between close points that are stored in the database or in any other form in the system. Data precision in most GIS systems is about meter on centimeter. One other fact that is needed to be considered regarding accuracy in data is called "Data Resolution". Data Resolution is "The degree to which closely related entities can be discriminated. Since a paper map is always the same size, its data resolution is tied to its scale. Resolution also limits the minimum size of feature that can be stored. "8 "Generally, a line cannot be drawn much narrower than about 1/2 a millimeter. Therefore, on a 1:20,000 scale paper map, the minimum distance which can be represented (resolution) is about 10 meters. On a 1:250,000 scale paper map, the resolution is 125 meters. Usually, it is desirable to specify the resolution of a dataset as a minimum feature size. For example, no lakes of less than 5 hectares surface area should be captured. In a GIS, this is the most important reason for having the same data represented at different scales."9 One other important fact that is needed to be considered is "Data Density"," Data density is a measure of how many features per area are stored, and may imply a minimum feature size. Greater density implies more features in a given area, and therefore the features may be smaller. The density of paper maps data is limited by its scale (and therefore its resolution). Areas (polygons) cannot be shown if they are smaller than the lines which draw them. For example, a polygon less than 250 meters wide cannot be drawn on a 1:250,000 scale map. This minimum size also limits the number of polygons that can be represented in a given area of a paper map. A GIS stores its data digitally, so the minimum size of a feature is limited only by the precision, which is effectively infinitesimal. Where the degree of detail in a coverage is arbitrary (e.g. soil polygons), a data definition or convention should specify the minimum size of features, and therefore their density, or resolution. Without this, different parts of the same coverage may have widely varying degrees of detail, influencing analysis results."10 And the final thing is "Data Detail". "Data detail is a measure of how much information is stored for each feature. A GIS stores lines (e.g., a lake shoreline) as a sequence of point locations, and draws it with the edges that join them. There is no limit to how many points can be stored, or how close together they may be. The amount of detail on line features should be limited just like data density. It does not make sense to store points at intervals which are shorter than the accuracy of their locations."11 References FPA, GIS Overview, GIS definition. available from http://www.fpa.nifc.gov/Library/Documentation/FPA_PM_Reference_Information/Output/GIS_overview.html#502291 INTERNET Data Sources for GIS available from http://www.colorado.edu/geography/gcraft/notes/sources/sources_f.html INTERNET Data Sources for GIS available from http://srmwww.gov.bc.ca/gis/gisscale.html INTERNET Read More