Data Input

Data input is the process of encoding data into computer-readable format and assigning the spatial data to a Geographic Information System (GIS). Spatial data input methods include manual digitizing, scanning, data conversion, keyboard entry, and coordinate geometry. The input method chosen depends upon several factors such as accuracy standards, form of output product needed and equipment availability. www.profc.udec.cl/~gabriel/tutoriales/rsnote/cp13/13-3-1 Digitization is the process of creating digital images/files or the entry of data into a computer in order to create a digital database. Digitization process seeks to capture, preserve, and disseminate images and data for public access. Existing maps can be digitized with a scanner or tablet digitizer. Raster data are obtained from a scanner while vector data are measured by a digitizer (See Figure 1).

Entering spatial data is more complicated than the attributes. One way to enter spatial information is to digitize, or manually enter the spatial coordinates by way of a mouse connected to a digitizing table or tablet. An operator traces the outline of polygons, such as land holdings, or along lines such as streams, or clicks the mouse on a point such as a water well. The table or tablet contains a fine grid of wires that capture the coordinates of where the mouse is located. GIS labs used to be filled with digitizing tablets. Why aren't the tablets as common today? First, over the decades since the 1970s, spatial data has been collected by organizations around the world, lessening the data input burden for today's GIS users. Second, other means may be more efficient than digitizing to collect spatial information, as will be discussed below. Third, the digitizing that is done today is often done right on the screen, using a mouse, in a process known as "heads-up digitizing." Most often, the data collector views a base map or image such an aerial photograph on the screen in a GIS, and traces features with a mouse on the screen. The features are saved in a new point, polygon, or line layer. Other means to enter data into a GIS besides digitizing include scanning. Maps are scanned by drum (roll) scanners or large format flatbed scanners. Once the data are scanned, they are in raster mode. If vectors are desired (for example, if the map contains streams), the data must be vectorized and tagged in an automated or manual process. Another means of input is via traditional surveying techniques, or with coordinates collected by Global Positioning Systems (GPS) receivers. Descriptions of land ownership, or parcels, can be entered in a process known as COGO, or coordinate geometry. Often, data such as imagery has been captured by a sensor on board an airplane or satellite, and that data can be brought directly into a GIS for analysis. Data that has already been collected can be downloaded from the Internet, such as from www.geographynetwork.com, or obtained on a variety of media, such as CD-ROMs. You will have the opportunity very soon to download data from the Internet for your GIS.

Data Output There are several ways of outputting data FROM your GIS. Displaying your data on the screen is the most common way of outputting data from a GIS, using maps symbolized as graduated colors, graduated symbols, charts, and so on. You have already had the opportunity this semester to output data in some of these ways. Printing is probably the second most common way of outputting your data. You have already created several layouts in ArcView, and will have the opportunity to create more. More and more, GIS users are outputting their data over the Internet, via Internet Map Server technology. Users of the technology can query and access just the data that meets their needs in an interactive mode using a standard web browser. We will be able to examine some of the sites that offer this service Data lineage is the ability to view a complete source-to-target flow, thru every process, every function, and every intermediate step. It illustrates what happens to a column, how it is used in expressions and when its name changes or when it is combined with another column to create something new. Data lineage helps decipher where a value came from, and how it was derived. Do your lineage reports have visibility into the “black boxes” that you are calling remotely? Would you like to “see” where the data flows when it goes “outside” the system? The IBM InfoSphere Metadata Workbench has a new capability called the Data Lineage Extender. This new feature lets me describe the details of any external process and include it in all of my metadata exploration and analysis. In this blog I try to focus on real-time issues, and so will start with the benefits of defining a remote Web Service; however, the Data Lineage Extender and the “Extension Mappings” that it offers are not limited to Web Services. Extensions, as they are also called, can be used to define external scripts, Stored Procedures, Java classes, COBOL programs, third party transformation tools — anything that you believe is important for completing your lineage picture.

Aerial photography is the taking of photographs of the ground from an elevated position. The term usually refers to images in which the camera is not supported by a ground-based structure.