Geodata Requirements
for Project Scoping and Environmental Analyses: Overcoming the Challenges
Philip Bailey
The geodata requirements for
environmental planning and management are both diverse and often poorly
communicated. Nobility is addressing
this perplexing issue by presenting the requirements, standards, and limitations
of geodata for a GIS-enabled expert decision support system. A variety
of topics are covered including the quality, spatial resolution, and precision
of vector data for typical project scoping analyses. This is complemented
by a description of suitable raster imagery frequently used for display
purposes and georeference. Nobility
uses Esri ArcView GIS software to support
environmental planning decisions, and this paper is aimed at helping to
remove confusion surrounding the often overwhelming task of collecting
and organizing geodata for this task.
Introduction
Environmental impact analysis typically involves
a strong spatial component. The occurrence and severity of an impact often
depends on the spatial relationship between an activity and the surrounding
environmental components. Spatial data files can be used to represent project
activities and the biological, physical, and socioeconomic components of
the environment that may be impacted by those activities.
Nobility
Environmental Software Systems has developed a commercial, general
purpose, decision support system for environmental analysis (see www.nobility.com/products
for a detailed description of this product). Nobility
EM is designed to connect ArcView GIS
map data with a knowledge base of information describing how environmental
impacts occur (Figure 1).
Figure 1. Nobility EM Project Map and Project
Explorer.
The knowledge base contains the definitions
of each environmental component type and possible activity that the user
is allowed to define. After the user has connected their geodata to the
appropriate knowledge base type, the Nobility
EM inference engine is used to interrogate the knowledge base and determine
the applicable environmental impacts (Figure 2). Environmental impacts
can be displayed either in a tabular or spatial context and interrogated
to determine their cause and meaning.
Figure 2 Nobility EM impact map and Impact Explorer.
The following sections describe the specific
ArcView
GIS data requirements for the
Nobility
EM system.
Visual Display
Not all spatial data are used to calculate
impacts; Nobility EM provides
for additional spatial data to be incorporated for display purposes only.
ArcView GIS
shapefiles can be used to represent Display Georeference Components. These
components are used for reference only and are not impacted by project
activities. An example of a georeference component is a file containing
district boundaries. Impacts do not occur on these boundaries but the boundaries
are included in the setting as a visual aid for users.
Scanned maps, aerial photographs, and satellite
images may also be added to a setting to improve the map display. These
types of spatial data are included as background information and are not
associated with components.
Spatial Data Specifications
To be used by Nobility
EM, spatial data must adhere to the following specifications for the
representation of components and activities, and the incorporation of imagery:
File Format:
-
Data should be stored as ArcView
GIS shapefiles (vector data model).
-
Use a separate shapefile for each component
and activity.
-
Do not include both roads and streams in the
same shapefile; rather, create two distinct shapefiles.
-
Do not have separate shapefiles for each type
of soil; rather, use one shapefile containing polygons for all soil types
and use the attributes of file to differentiate among different soil types.
-
Data should be clean (i.e. no dangles)
Shape Type:
-
Shapefiles should contain closed polygons,
lines, or points.
-
Avoid using polylines for polygon features
- impacts should be calculated for the area within a polygon feature and
not just for the outline.
Attributes:
-
Activity and component characteristics can
often be incorporated into the feature attribute table (FAT) of a shapefile,
reducing the amount of manual entry required by the end-user. Characteristics
defined by attributes of the shapefile are called spatial characteristics
in Nobility EM.
Spatial Extent and Resolution:
-
Shapefiles should have a resolution and extent
appropriate to the study area. Consider clipping shapefiles containing
data well outside the boundary of your setting.
Projection/Coordinate System:
-
All shapefiles should use a consistent projection
and datum such that they can be loaded into a single ArcView
GIS view and be properly aligned.
Imagery
File Format:
Any file format supported by ArcView
GIS may be added to a Nobility
EM setting as a background image.
Metadata Requirements
Standard metadata requirements apply for the
geodata used in Nobility EM.
Examples of useful metadata include description, spatial domain, data quality,
entity, and attribute information (attribute values and definitions).
In addition to the standard metadata, it
is recommended that information about how the geodata is used in Nobility
software be recorded and maintained.
Acknowledgements
Thank you to the Heather Alexander, Chris
Clibbon, Monique Cornish, George Davis and Dennis Radage of Nobility for
their advice and comments during the preparation of this paper.
Contact Information
Philip Bailey
Software Development Engineer
Nobility
Environmental Software Systems Inc.
Suite 300 1765 West 8th Avenue
Vancouver BC V5Y 1S3
Canada
pbailey@nobility.com
Tel: (604) 733-2996
Fax: (604) 733-4657