GIS Overview

This section provides an overview of GIS (Geographic Information System) and a list of websites and other resources for more detailed information. For information specific to FPA-PM, see the GIS Requirements for FPA-PM section.

GIS is a computer system designed for capturing, storing, integrating, analyzing and displaying data from a geographic perspective. GIS is comprised of the following elements:

• Technology that is used to analyze features that make up the earth's surface
• System that includes software, hardware, data, and personnel
• Use of the relative location of features in x, y, and z space to establish relationships between features

  Typically, GIS stores information in themes or layers that hold data about a particular kind of feature. Each layer is linked to a specific position on the globe.

GIS Thematic Layers and Data Sets

GIS organizes geographic data into a series of thematic layers and tables. Because data in a GIS are referenced to geography, they have real-world locations and could overlay one another. GIS links the location to each layer (such as people to addresses, buildings to parcels, or streets within a network) to give a better understanding of how the features interrelate.

In a GIS, collections of geographic features are organized into data sets, such as land parcels, fire locations, buildings, orthophoto imagery, and raster-based digital elevation models (DEMs). Precisely defined geographic data sets are critical for useful geographic information systems, and the layer-based concept of thematic collections of information is critical for GIS data sets.

Figure 1- Types of Spatial Data

Data sets can represent the following information:

• Raw measurements (such as satellite imagery)
• Compiled and interpreted information
• Data derived using geoprocessing operations for analysis and modeling

  Many of the spatial relationships between layers can be easily derived through their common geographic location. GIS manages data layers as specific objects and uses a wide collection of tools to work with the data layers to derive key relationships.

Vector Data Types

Vector data is composed of discrete coordinates that can be used as points or connected to create lines and polygons. Coordinates for fire data are typically provided in geographic format (latitude/longitude) or projected (typically UTM for the lower 48 states; Alaska uses the Albers projection):

• Points: Discrete location on the surface of the planet, represented by an x-y coordinate pair. Each point on the map is created by latitude and longitude coordinates, and is stored as an individual record in the shapefile. (See .)

Figure 2- GIS Points

• Lines: Formed by connecting two data points (See ). The computer reads this line as straight, and renders the line as a vector connecting two x-y coordinates (X = longitude, Y = latitude). The more points used to create the line, the greater the detail. FPA requires that the line and polygon features include topology. For lines, this means that the system stores one end of the line as the starting point and the other as the end point, giving the line "direction".

Figure 3- GIS Lines

• Polygons: An area fully encompassed by a series of connected lines. Because lines have direction, the system can determine the area that falls within the lines comprising the polygon. Polygons are often an irregular shape. Each polygon contains one type of data (e.g., vegetation, streets, and dispatch locations would be different polygons). All of the data points that form the perimeter of the polygon must connect to form an unbroken line. When preparing files for FPA, verify that the polygons are closed. (See .)

Figure 4- GIS Polygons

Raster Data Types

Raster data represent features as a matrix of cells within rows and columns in continuous space. These cells are formed by pixels of a specific dimension size, and can be described as either "cell-based" or "image-based" data.

Cell-based Data

Each raster data layer represents one attribute. Most analyses combine these layers to create new layers with new cell values, as either continuous or discrete data. Continuous data types have gradations, such as temperature or elevation. Discrete data types have clearly delineated boundaries, such as a city boundary or specific vegetation type.

The cell size used for a raster layer affects the results of the analysis and how the map looks. Using too large a cell size will cause some information to be lost. Using too small a cell size will significantly increase the storage space and processing time required, without adding precision to the map. To create an effective cell size, base the cells on map scale and on the minimum mapping unit of the other GIS data.

Figure 5- Cell-based Raster Data

Image-based Data

Image data ranges from satellite images and aerial photographs, to scanned maps that have been converted from printed to digital format.

Figure 6- Image-based Raster Data

Grid Data

The grid provides the simplest way of dealing with the data. Grids speed the calculation time required for the computer to determine the location of the data points within the polygon. For example, elevation data are stored in this layer. (See .)

Figure 7- Grid Cell Data

Attributes

Attribute (tabular data) is descriptive data that GIS links to map features. For example, attributes of a dispatch location, which is represented by a spatial point, might include an engine bay that accommodates a certain number of engines, crews, dozer pads, and so on. These attributes are stored in a database and relate to the feature using a primary key (unique identifier).

Database

The database forms the foundation of the GIS system. All the information about the GIS system is stored in the database. The first 5 fields of every GIS database for FPA always contain the same type of information, and provide a way to link each record with a unique identifier.

Topology

Topology describes the spatial relationships between adjacent features, and uses x, y coordinates to identify the location of a particular point, line, or polygon. Using such data structures enforces planar relationships, and allows GIS specialists to discover relationships between data layers, to reduce artifacts from digitization, and to reduce the file size required for storing the topological data.
(See Types of GIS Topology for examples of different topologies.)

Figure 8- Types of GIS Topology

GIS Shapefiles

A shapefile is a type of GIS data layer that is used to transfer vector data. Each shapefile can contain only one feature class. While less robust than coverages, shapefiles tend to be significantly smaller, which reduces processing time. For FPA-PM, shapefiles are stored as a set of related files, which must be moved and stored as a group in order for the data to be interpreted correctly. For FPA, use the *.zip file format to transfer information about the FMUs.

Geodatabases

Geodatabases are object-oriented data models that are stored in a relational database management system. They enable you to store multiple feature classes and the topological relationship among them. All feature classes in a feature data set must share the same spatial reference. Geodatabases have the ability to implement sophisticated business logic that can build relationships between data types, validates data, and controls access (import, editing, & export).

Power of GIS

The analytical power of GIS comes from its ability to overlay and match different shapefiles for the same geographic area, which enables you to visualize the interactions among the different data. For example, you may have one shapefile that contains lightning strikes and other weather data, one that contains ignition locations, one that shows human habitation, and one that contains vegetation coverage. By overlaying these files, you can quickly see the correlations among all these factors, which then enables you to develop a more effective fire management plan.

Uses of GIS

GIS enables you to perform several levels of analysis. At its lowest level, GIS enables you to inventory the location of resources on the landscape. At the next level, you can analyze relationships among various features. Modeling is the highest level of analysis. Because GIS provides a spatial reference for the data being evaluated, it is a powerful tool for modeling events and scenarios that have occurred or could occur.

The following examples are some of the most common uses of GIS:

• Inventory of where all the engine bays are located
• Identification of what type of vegetation is located where, along with slope, aspect, elevation, and the presence of water
• Impact of human habitation on the environment, e.g., disruption of animal migration pathways, wildland-urban interface, effect of mining on stream quality, roads and trails
• Effect of environmental disasters on the landscape, e.g., erosion patterns after a large fire, fallout area from a volcanic eruption, areas of devastation after a tsunami or hurricane
• Analysis of transportation routes and networks
• Analysis of optimum placement for telephone, data, and power lines
• Urban planning
• Modeling "what-if" scenarios for strategic and tactical training, e.g., evacuation routes and plans in case of natural disaster

References

• Bureau of Indian Affairs. http://www.bianifc.org/gisgps.html
• Bureau of Land Management GIS team. http://www.or.blm.gov/gis/
• ESRI. http://www.esri.com. Two relevant papers include:
  • System Design white paper: http://www.esri.com/library/whitepapers/pdfs/sysdesig.pdf
  • Enterprise GIS data management:
    http://gis.esri.com/library/userconf/proc01/professional/papers/pap742/p742.htm
• Forest Service. http://www.fs.fed.us/gstc/
• Geoplace.com. http://www.geoplace.com/
• Geospatial Solutions. http://www.geospatial-online.com/geospatialsolutions/
• GIS.com. http://www.gis.com/
• Haithcoat, Tim.
  http://msdisweb.missouri.edu/presentations/intro_to_gis/pdf/GIS_intro_over.pdf
• Mapmart. http://www.mapmart.com/
• National Park Service. http://www.nps.gov/gis/
• Silvis. Wildland-Urban Interface. http://silvis.forest.wisc.edu/library/wuilibrary.asp
• US Fish and Wildlife Service. http://www.fws.gov/data/gishome.html

Related Topics

• GIS Requirements for FPA-PM
• Land Management Objectives
• Constraints
• Weighting
• Wildland Fire Use
• Importing shapefiles into FPA-PM
• Setting up FMU