Geographical Information Essay, Research Paper

GIS

By:fazil

Geographical 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. STEP1 -

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 10:00am to 2:00pm 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 gis 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 were

taken 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 cliché "many

hands make light work". In short, GIS is a relatively new

approach to organize data. The data is organized logically as

well 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.