Chapter 5: Geospatial Data

CHAPTER 5 OUT LINE  GEO SPATIAL DATA DATA CAPTURING AND DATA ENTRY SOURCES OF SPATIAL DATA ERRORS AND ITS CORRECTION MEASURES Data Sources and data capturing What is Geospatial Data?  The word geospatial is used to indicate that data that has a geographic component to it.  T...

CHAPTER 5 OUT LINE  GEO SPATIAL DATA DATA CAPTURING AND DATA ENTRY SOURCES OF SPATIAL DATA ERRORS AND ITS CORRECTION MEASURES Data Sources and data capturing What is Geospatial Data?  The word geospatial is used to indicate that data that has a geographic component to it.  This means that the records in a dataset have locational information tied to them such as geographic data in the form of coordinates, address, city, or ZIP code.  GIS data is a form of geospatial data. Source of data The main Sources of data are  Field survey data  Existing tabular data and map data Remote sensing data aerial photographs and satellite imagery Soft idea/undocumented knowledge GIS data capturing and data entry techniques A, Data Capture GIS Data Capture is a method where the data on different map attributes, facilities, resources, and organizational information are digitized and organised on an objective GIS system in appropriate layers. GIS Data Capture Methods: Basically, two types of methods are generally used for Data Capturing in GIS: 1. Primary GIS Data Capture Method. 2. Secondary GIS Data Capture Method. 1. Primary GIS Data Capture Method: The Primary GIS Data Capture Method used surveying technologies to capture data using Raster Data Capture or Vector Data Capture. CONT’D I. Raster Data Capture Method: The raster GIS data capture technique involves capturing of attributes and other data without physical contact. This is usually done with the help of Satellite Imaging Techniques and Aerial Photography. The advantage of this GIS Data Capture Method is that there is a consistency in the data generated and the whole process can be regularly and systematically organized to get the most accurate data in a very cost-effective manner. CONT’D II. Vector Data Capture Method: Capturing of datasets through physical surveying techniques such as Differential Global Positioning System (DGPS) and Electronic Total Station (ETS). Although this technique is the most effective process to obtain accurate results on the target GIS system, it is more time consuming and costly. CONT’D 2.Secondary GIS Data Capture Method: The Secondary GIS Data Capture Method used technologies such as scanning, manual digitizing, vectorization, photogrammetry, and feature construction to Capture Data. Scanning Raster Data: High resolution scanners give very accurate raster images from the hard copies, which then can be Georeferenced and Digitized to get the Vector output. Digitizing: Digitizing is a process of entering digital codes of analyzed data into computer. Digitizing can be manual (using digitizing tablet) or automatic (using scanner). CONT’D B. Data Entry Data input is the procedure of encoding data into a computer- readable form and writing the data to the GIS data base. There are two types of data to be entered in a GIS - spatial (geographic location of features) and non-spatial (descriptive or numeric information about features).  There are three types of data entry: 1. Manual (via typing on keyboard or importing text files); 2. Digitizing; 3. Scanning; CONT’D Data input covers the range of operations by which spatial data from maps, remote sensors, and other sources are transformed into a digital format.  Among the different devices commonly used for this operation are keyboards, digitizers, scanners, and interactive terminals or visual display units (VDU). Given its relatively low cost, efficiency, and ease of operation, digitizing constitutes the best data input option for development planning purposes. CONT’D Two different types of data must be entered into the GIS: geographic references and attributes. Geographic reference data are the coordinates ( in terms of latitude and longitude) which give the location of the information being entered. Attribute data associate a numerical code to each cell or set of coordinates and for each variable, either to represent actual values (e.g., 200 mm of precipitation, 1,250 meters elevation). Data input routines, whether through manual keyboard entry, digitizing, or scanning, require a considerable amount of time. CONT’D C. Data Storage Data storage refers to the way in which spatial data are structured and organized within the GIS according to their location, interrelationship, and attribute design. Computers permit large amounts of data to be stored, either on the computer's hard disk or in portable diskettes. CONT’D D. Data Manipulation and Processing Data manipulation and processing are performed to obtain useful information from data previously entered into the system.  Data manipulation embraces two types of operations: (1) operations needed to remove errors and update current data sets (editing); and (2) operations using analytical techniques to answer specific questions formulated by the user. The manipulation process can range from the simple overlay of two or more maps to a complex extraction of disparate pieces of information from a wide variety of sources. CONT’D E. Data Output Data output refers to the display or presentation of data employing commonly used output formats that include maps, graphs, reports, tables, and charts, either as a hard- copy, as an image on the screen, or as a text file that can be carried into other software programs for further analysis. Data management and analysis Required to facilitate the data input, storage, management, retrieval, analysis and presentation The general procedure for a GIS project includes Determining the objectives of the GIS project  Designing the database Building/creating the GIS database Entering data Analysis of the data Presentation of the analysis result or information. Cont’d Data management is the practice of collecting, keeping, and using data securely, efficiently, and cost-effectively. It is the process of ingesting, storing, organizing and maintaining the data created and collected by an organization. Managing data effectively requires having a data strategy and reliable methods to access, integrate, cleanse, govern, store and prepare data for analytics. Data management skills are the abilities you use to effectively manage and use information. The main sources of spatial data errors and its correction measures Errors can be injected at many points in a GIS analysis, and one of the largest sources of error is the data collected. Each time a new dataset is used in a GIS analysis, new error possibilities are also introduced.  One of the feature benefits of GIS is the ability to use information from many sources, so the need to have an understanding of the quality of the data is extremely important. CONT’D There are many sources of error that may affect the quality of a GIS dataset. Burrough (1986) divides sources of error into three main categories: Obvious sources of error. Errors resulting from natural variations or from original measurements. Errors arising through processing. CONT’D Errors Arising Through Processing Processing errors are the most difficult to detect by GIS users and must be specifically looked for and require knowledge of the information and the systems used to process it. These are subtle errors that occur in several ways, and are therefore potentially more insidious, particularly because they can occur in multiple sets of data being manipulated in a GIS project. cont’d Sources of Errors in GIS Data Conception Measurement Representation Analysis GIS data error can be corrected in different ways such that careful data collection and through editing.I In general good data management techniques is used to control the occurance of error in gis data.