The Forestry Source - October 2011 - (Page 14)
GIS for Foresters
Standardizing Species Codes Using the NRCS PLANTS Database
user databases built on files, up to larger workgroup, department, and enterprise geodatabases accessed by many users. Geodatabases have a comprehensive information model for representing and managing geographic information. This model is implemented as a series of tables holding feature classes, raster datasets, and attributes. In addition, advanced GIS data objects add GIS behavior, rules for managing spatial and attribute integrity, and tools for working with numerous spatial relationships of the core features and attributes. Attribute domains are rules that describe the legal values that can be contained in a field. They provide a method of enforcing data integrity in that they constrain the values allowed in a particular attribute for a table or feature class. Whenever a domain is associated with an attribute field, only the values within that domain are valid for the field. In other words, the field will not accept a value that is not in that domain. Using domains helps ensure data integrity by limiting the
Figure 1: In the Table to Table dialog box, specify the Output Location for the target (output) geodatabase and the Output Table name for the table being created.
By Tim Clark orestry, like many other disciplines, has its own set of nomenclature, including abbreviations and coding conventions that are used to identify managed features. Moreover, forestry idioms are often specific to geographic regions and organizations. When a specific “lingo” is applied to a GIS database, these local variations are often incorporated as quasi-standards that only local users can understand. This may not be an issue until the data is shared or published, when other users who do not have the same local knowledge try to use the data. Variations are especially common in tree-species codes, taxonomy, and common names. If a standard convention, common within the industry were applied to the database, the spatial data would be more open and understandable. But whose standard should be adopted? This article outlines the important pieces of code needed to standardize a portion of the ArcGIS geodatabase and highlights the technical steps needed to use a national set of species codes.
As a standard, I recommend using the PLANTS Database published by the US Department of Agriculture’s Natural Resources Conservation Service (http:// plants.usda.gov). The NRCS PLANTS database provides standardized information about the vascular plants (trees, shrubs, grasses, etc.), and nonvascular plants (mosses, liverworts, hornworts, and lichens) of the United States and its territories. The database is easy to search, and data can be downloaded as uncompressed ASCII text. Using the same plant taxonomy, domains, and feature classes to set up the forester’s geodatabase enforces data integrity, ensures consistent data collection, and supports data access. Inside a Geodatabase An ArcGIS geodatabase is a collection of geographic datasets of various types. The datasets are managed in either a file folder hierarchy or a relational database. The geodatabase is the native data source for the ArcGIS and is used for editing, data automation, spatial analysis, and cartographic production. Geodatabases come in many sizes; have varying numbers of users; and can scale from small, singleThe Forestry Source
choice of values for a particular field; it also eliminates the potential for errors and inconsistencies caused by typographic errors, spelling, and abbreviations. Coded value domains are managed as properties of the geodatabase. They are stored in the geodatabase tables and can be used on any number of attribute fields in any feature class or table stored in the geodatabase. They are managed as sets of code. These sets of code are description pairs with code values stored in the attribute field. A description is displayed any time the user accesses the values of a field. Using the NRCS PLANTS Database to standardize coding conventions, value domains, and feature classes makes sense because the database is proven and well known within the industry. Best of all, its standards can be directly into a GIS and used wherever plant taxonomy is referenced using geodatabase coded-value domains. Below is an explanation of how to download a tree species list for an area from the NRCS PLANTS Database and create a coded value domain that can be used anywhere tree species are referenced in a GIS. Create Tree Species Domains The process described below allows an ArcGIS user to incorporate standard species codes and scientific names into an ArcGIS geodatabase. Once these are applied, users are presented with a pulldown list of valid values, rather than a
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