Ardmore GIS

ArcIMS Interactive Mapping

What is G.I.S.?

G.I.S. is an acronym for Geographic Information System. A G.I.S. is able to store & retrieve tabular information as well as spatial (locational) information about an object or feature. It allows for creating not only "pretty" maps, but maps that help make informative decisions about a situation or problem. The creation of maps has been around since one person tried to show someone else where something was by drawing a picture of how to get from here to there. Since that time technology has allowed us the luxury of integrating that basic principal into almost every aspect of daily life. Maps have become a necessity in daily life as we try to keep track of more & more information. G.I.S. does not take the place of any C.A.D. or database system but simply is a good example of synergy, or the whole is greater than the sum of its parts.

Database Analysis & Management

dbf, Excel, Access, Oracle, etc...

G.I.S.

ArcInfo, ArcView, AutoCadMap, MapInfo, etc...

Computer Aided Drafting (C.A.D.)

AutoCAD, Microstation, ect..

G.I.S. produces a “SMART MAP” that is geospatially correct & has data associated with certain features that can be queried. Each feature in a G.I.S. map has a corresponding record that stores attributes related to that feature. When this is implemented correctly it enables the end user to quickly retrieve information based on attribute data or spatial location. For example when the city needs to determine how many fire hydrants have a flow rate greater than 1000 gallons of water a minute, the G.I.S. can quickly & accurately deliver this information with just a few clicks of a mouse. However, a database can also produce this information as quickly. If the city also want to see how many fire hydrants are within 500' of a building a C.A.D. system would allow for this. Integrating these two processes is where the G.I.S. differentiates from either a database or a C.A.D. system. A G.I.S will allow the user to determine how many buildings greater than 10,000 sq ft have a fire hydrant closer than 500' with a flow rate greater than 1,000 gallons per minute and also be able to create an accurate map of these features based on these pre-defined attributes With the ability to have more information available in a format that allows for rapid retrieval the G.I.S. allows better decisions to be made with regards to the planning, implementing, maintaining, & managing a city.

Data Capture

There are several methods of entering information into a G.I.S. First there must be a good established coordinate system with a set of control points. This is the basis upon which all other data layers will be referenced, therefore the accuracy of this dataset is critical. Other data layers can be created, imported, compiled, scanned, or collected in order to get the information into the G.I.S. Some examples of this include importing existing digital plats & plans from engineers, drawing in building footprints from orthophotography, collecting data in the field with G.P.S., importing tabular information from existing databases, or drawing features in using coordinate geometry (COGO). Background images can be imported into the G.I.S. through either scanning paper drawings or digital photography & then some degree of rectification (alignment of the image based on control points).

Scale

Map scale is basically the distance ratio between features on a map & the corresponding features on the ground. This relationship determines how much ground area can be portrayed on a specific size of paper. There are different ways to calculate scale but here are some of the easiest formulas for simple conversions.

*Basic Formulas for Determining Scale*	*Examples of Different Scale Types*
MD = Map Distance MS = Map Scale *GD = Ground Distance (MD) x (MS) = GD (GD) / (MD) = MS (GD) / (MS) = MD	Unit Scale 1" = 100' (1 inch equals 100 feet) Ratio or Representative Fraction (RF) Scale 1:1200 (1 unit on the map represents 1,200 units on the ground) Graphical Scale

Vector / Raster data

Vector Data

Raster Data

Vector data is comprised of three basic geometric elements, being points, lines, & polygons. A firehydrant can be stored as a point, a street centerline can be stored as a line, & a building can be stored as a polygon. Most features can be stored using this format. This geometric structure allows for rapid & precise measurements & calculations. C.A.D. drawings along with shapefiles are stored in this manner which allows for very clean, clear line work elements.

Raster data is primarily imagery data. It is comprised of rows & columns of cells with certain values assigned to each cell. The resolution of the final image is determined by how many rows & columns there are in an image. Its usage can range from base photography to satellite imagery, from scanned maps to terrain modeling. Raster data is a good back drop to vector data along with being the basis upon which some vector data is created. Imagery data can also be used for remote sensing & rapid land use classification. With the ability to store & analyze infrared, visible, & ultra-violet spectral bands some patterns, features, & structures can be much easier to identify. Different combinations of the these bands also allow for other forms of analysis.

©Copyright 2004, City of Ardmore, G.I.S. Dept.
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