Data In A Gis System example essay topic

GIS By: fazilGeographical Information System - GIS What is GIS? GIS is an emerging method of data storage and interpretation. GIS is, simply put a database. It is many tables of data organized by one common denominator, location. The data in a GIS system is organized spatially, or by its physical location on the base map. The information that is stored in the database is the location and attributes that exist in that base map, such as streets, highways, water lines, sewers, manholes, properties, and buildings, etc. each of these items don? t just exist in the database, the attributes associated with the item is also stored.

A good example of this would be a specific sewer line, from and arbitrary point A to a point B. Ideally, the sewer line would be represented graphically, with a line connecting the two points or something of the like. When one retrieves the information for that line in particular, the attribute data would be shown. This data would include the size of pipe, the pipe material, the upper invert elevation, the downstream invert elevation, the date installed, and any problem history associated with that line. This is the very gist of what a GIS system is.

How is a GIS system created? Building a GIS system from the ground up is a very time consuming and extremely expensive venture. This is why only large metropolitan areas have developed or are developing GIS systems. STEP 1 -Determining and acquiring a base map Since a GIS system is basically a digital map, the extents of the map have to be determined. Once the area of interest is decided, the base map has to be built. This is done using aerial photography (digital orthography).

This type of photography is very high definition, and of consistent scale (all photographs are taken from almost exactly the same altitude). The photography that is done is difficult. Times when photographs are able to be taken are few. For instance, time is limited to the winter months due to less foliage, and from 10: 00 am to 2: 00 pm to reduce the shadows. STEP 2 - Digital Overlay Once the base maps have been acquired, the time consuming work begins. Each digital map section has to be gone over by a person on a computer.

That person outlines each object to be included in the gas system. These objects are the same as the ones stated previously (like sewer lines, water lines, etc. ), although they are not limited to those. Along with all of the physical information that is entered into the database, there is a lot of other physical information to be added that is not reflected on the aerials, such as property lines, tax and voting districts, as well as zoning districts. STEP 3 - Data entry Following the design and creation of the basic data skeleton, the actual data need be entered.

This includes all of the attribute data for all hydrants, sewer lines, water lines, properties, buildings, streets, highways, creeks, etc. this portion of the process is the most time consuming. The bulk of the data to be entered is on paper, and there is no easy way to convert it to digital other than manual data entry. One issue in this step that is worth noting is the importance of the quality control. As the data is entered, errors become inherent.

In order to keep these at a minimum, an effective quality control system needs to be in place to maintain data integrity. STEP 4 - Application Development Once all the information is entered (which never happens since the aerial photographs become outdated in about one month), the core data is placed on a file server for the different agencies to access. At this stage each agency usually directs some resources into application development. Since the structure and organization is very generic, so all agencies can use it, each entity develops applications for the data that is better suited for their purposes. For example, the metropolitan sewer district would focus on the ability to query and store data relating to the sewer system, since it is their main focus.

The county auditor would begin to restructure its file system and information management system to incorporate GIS into their organization, as well as developing tools within the GIS system to streamline the commands to suit them. STEP 5 -Continuous Improvements; Updates Since GIS is a database that is based upon land use, it is easy to realize how much in the way of resources must be expended just to keep the data current. Consider new construction. Every house and building that has been erected since the initial aerial photographs we retaken are not contained within the data.

This information, along with much more needs to be updated daily, and on a large scale. For large metropolitan areas, such as Cincinnati, each agency is responsible for keeping current the data that applies to them, i.e. the sewer district keeps the information regarding the sewer system up to date. This occurs for two reasons. 1.

They are the agency that needs the data current most. This way they can make sure the data is current as well as correct. 2. It reduces the workload of updating the system by dividing it up into small portions, similar to the clich'e 'many hands make light work'. In short, GIS is a relatively new approach to organize data.

The data is organized logically a swell as visually which is about as user friendly as it gets. GIS also saves time and money. An example of this would be a water leak in the city water system. Before GIS the crew that would respond to the leak would first go to the drawings section of the main office to get accurate drawings of the area in question. This would be time consuming as well as a waste of resources. GIS would enable the responding crew to be outfitted with a laptop computer containing part of the GIS data.

The crew would be able to respond directly to the leak, saving money and resources.