GIS Analysis Functions

Outline

1. Spatial Data Functions
2. Attribute Functions
3. Integrated Analysis of Spatial and Attribute Data
4. Cartographic Modeling
• Entirely in the Raster Domain
• Ability to form a logical sequence
• Map Algebra
5. Connectivity Functions
• Contiguity Measures
• Proximity Function
• Network Functions
• Sets of Constraints
• Seek or Stream Functions
• Intervisibility Functions
6. Output Functions
• Map Annotation
• Line Styles
• Various Graphic Systems

CARTOGRAPHIC MODELING

Definition of Cartographic modeling: The use of basic GIS functions in a logical sequence to solve complex spatial Problems. It was developed to model land use planning alternatives, and applications that require the integrated analysis of multiple geographically distributed factors. Coined by Dana Tomlin in 1983.

Entirely in raster domain. Due to the additive (or subtractive) nature of analysis the raster format with assigned values inherent to the data is utilized. Digitized data is layered, and these layers are combined to construct constraint maps that then can be subjectively analyzed as to the best alternative.

Ability to form a logical sequence. The process of cartographic modeling is characterized by working backward through the process to insure that all data that will be needed are identified. Data that will not be used therefore will not be collected. This backward procedure insures that any judgments to be made are explicitly identified. Subjective judgments are an integral feature of cartographic modeling.

Map Algebra. i. e. (Map #1 + Map #2) / (Map #3 * Map #4). This is one of the basic concepts of GIS. Maps have VALUE. The distance from Chicago to Omaha is not just 500 miles, it is \$. 45 cents per mile on the interstate road system, it is \$ .67 cents per mile on the roads around the DOT (department of transportation) scales. The fine for being caught overloaded is \$500.00. 32% of truckers driving the roads to avoid the scales get caught by mobile DOT patrols. What is the cheapest way to get to Omaha from Chicago?

Example of programs that use Cartographic Modeling; Map Factory, ADDRESSEE, Grass, and MAP II.

CONNECTIVITY FUNCTIONS

Contiguity Measures. Contiguity measures evaluate characteristics of spatial units that are connected. These units share one or more characteristics with adjacent units and form a group. The term UNBROKEN is the key concept. Different adjacent features may have more than one attribute but they must all have a COMMON attribute to be considered as reflecting contiguity.

Contiguity is used to measure shortest and longest straight line distances across and area and to identify areas of terrain with specified size and shape characteristics.

Example. An area of continuous pastureland with an area of no more than 10 acres with no part of it wider than the sound of the Acme Pig Call can be heard.

Proximity Functions. The simple distance between features, commonly units of length but can be other units such as how far away the ACME PIG CALL can be heard.

Four parameters are used to measure proximity. 1. target locations. 2. unit of measurement. 3. a function to calculate proximity. 4. and the area to be analyzed.

A common type of proximity analysis is the buffer zone. Coverage can be quit complicated involving many layers and mathmaticaly complex such as the decreasing sound levels due to the inverse proportion law of noise generated by various types of air traffic in the vicinity of a housing area.

Network Functions

Definition: A network is a set of interconnected linear features that form a pattern or framework. They are commonly used for moving resources from one location to another. City Streets, Power Transmission Lines, and Airline Service Routes are examples.

There are three principal types of GIS Analysis performed by Networking. 1. Prediction of loading on the network itself (prediction of flood crests), rate optimentation (emergency routing of ambulances), and resource allocation (zones for servicing rescue areas).

Networks analysis entails four components. 1. set of resources (goods to be delivered). 2. one or more locations where the resources are located (several warehouses where the goods are located). 3. an objective to deliver the resources to a set of destinations (customer locational data base). 4. Set of constraints that places limits on how the objective can be met (is it economically feasible to deliver pizzas to Lincoln from a store in Omaha ?).

The Spread Function is simply the "best" way to get from point A to point B. "Best" can be fastest, it can be most the most economical, or a subjective measurement such as most scenic. It is an evaluation of phenomena that accumulates with distance.

Imagine a square and you are going to travel from the lower left corner to the upper right corner. The straight line distance is 1.414 times the side of the square, and the distance across the sides is 2.0 times the length of a side. If this square represented a pasture containing angry buffaloes it would probably beneficial to walk around the fenced perimeter and go the extra distance.

Output of this particular GIS functions is sometimes referred to as ACCUMULATION SURFACE or FRICTION SURFACE. These concepts refer to the "effort it takes to get from A to B, such as the square traversed was knee deep mud (or a lake) across the diagonal but dry at the perimeter. It would be farther, but easier to again go the extra distance.

Seek or Stream Functions

Seek and Stream are synonymous and refer to a function that is directed outward in a step by step manner using a specified decision rule. This procedure is initiated and proceeds until the any further movement violates the decision rule.

This GIS function, as an example, could be used to evaluate erosion potential. The decision rule in this case would be elevation. As the process proceeds outward from the source (rainfall), the decision will always proceed down hill, never uphill. The path of least resistance best describes this function, Sea level, interior drainage or the edge of the area analyzed causes the function to terminate.

Intervisibility Functions

This GIS function is typified by the phrase LINE OF SIGHT. It is a graphic depiction of the area that can be seen from the specified target areas. Areas visible from a scenic lookout, or the required overlap of microwave transmission towers can be mapped using this procedure. Intervisibility functions rely on digital elevation data to define the surrounding topography. Applications such as landscape layouts, military planning, and the obvious communication utilization are best serviced.

The output of this function is somewhat unique in that it is often displayed in a SIDE VIEW format. The vertical field of view and maximum viable distance are the component parameters.

It is powerful tool for trial and error analysis in which the placement of objects can constantly be re-evaluated. Offshoots of this type of procedure can produce graphics that exhibit three dimensional perspective. SHADED RELIEF IMAGES or SHADED RELIEF MODELS, along with PERSPECTIVE VIEWS are valuable presentational tools. The process called draping is used to apply another data set over this shaded depiction to further enhance presentability.

OUTPUT FUNCTIONS

Map Annotation

Definition: Titles, Legends, Scale Bars, and North Arrows are the simplest forms of depicting information concerning the map.

The various programs available usually handle this as user input and it is not generated by the software. Flexibility as to location (position), fonts, symbology, and size are varied as to the individual programs. Text labels are an important aspect of map viewing and are all different as to program. Sophistication is increasing and actual hard copy maps can be enhanced with secondary software applications.

Texture Patterns and Line Styles

Texture patterns and line styles are difficult to alter from program guidelines so initial analysis of the output should be considered when choosing a software.

Graphic Symbols

Graphic Symbols are used to portray the various entities depicted on the map. Some software packages provide a simple standard symbol set, but do not allow user input, others store them within the GIS and they can be called to use as needed, others assign a symbol to an attribute and allow the symbology to be automatically plotted. As before the selection of the software and its application should be carefully considered as to the output presentation needed.

NOTE: please see Chengdai Liu's page for last three parts.

Submitted by Michael L. Hauschild.