Describing data

Geoprocessing tools work with all types of data, such as geodatabase feature classes, shapefiles, rasters, tables, topologies, and networks. Each piece of data has particular properties that can be accessed and used to control the flow of a script or used as the parameters of a tool. For example, the output feature type of the Intersect tool is dependent on the shape type of the data being intersected, that is, point, line, or polygon. When the Intersect tool runs in a script on a list of input datasets, you must be able to determine the shape types of the input datasets so the correct output shape type can be set. You can use the Describe function to determine the shape types of all the input datasets.

Using the Describe function, a dataset's properties can be determined and used to make decisions. For instance, in the following example, the script uses Describe to evaluate the shape type (polyline, polygon, point, and so on) of input data and determine which geoprocessing tool is appropriate.

import arcpy

inFC = arcpy.GetParameterAsText(0)
outFC = arcpy.GetParameterAsText(1)

# Describe a feature class
#
desc = arcpy.Describe(inFC)

# Get the shape type (Polygon, Polyline) of the feature class
#
type = desc.shapeType

# If the shapeType is Polygon convert the data to polylines 
#  using the FeatureToLine tool, otherwise just copy the 
#  data using the CopyFeatures tool.
#
if type == "Polygon":
    arcpy.FeatureToLine_management(inFC, outFC)
else:
    arcpy.CopyFeatures_management(inFC, outFC)

The Describe function returns a Describe object, with multiple properties, such as data type, fields, indexes, and many others. Its properties are dynamic, meaning that depending on what data type is described, different describe properties are available for use.

Describe properties are organized into a series of property groups. Any particular dataset acquires the properties of at least one of these groups. For instance, if describing a geodatabase feature class, you could access properties from the GDB FeatureClass, FeatureClass, Table, and Dataset property groups. All data, regardless of the data type, always acquire the generic Describe Object properties.

• Describe Object properties
• ArcInfo Workstation Item properties
• ArcInfo Workstation Table properties
• CAD Drawing Dataset properties
• CAD FeatureClass properties
• Cadastral Fabric properties
• Coverage FeatureClass properties
• Coverage properties
• Dataset properties
• dBASE Table properties
• Editor Tracking properties
• FeatureClass properties
• File properties
• Folder properties
• GDB FeatureClass properties
• GDB Table properties
• Geometric Network properties
• LAS Dataset properties
• Layer properties
• Map Document properties
• Mosaic Dataset properties
• Network Analyst Layer properties
• Network Dataset properties
• Prj File properties
• Raster Band properties
• Raster Catalog properties
• Raster Dataset properties
• RecordSet and FeatureSet properties
• RelationshipClass properties
• RepresentationClass properties
• Schematic Dataset properties
• Schematic Diagram properties
• Schematic Folder properties
• SDC FeatureClass properties
• Shapefile FeatureClass properties
• Table properties
• TableView properties
• Text File properties
• Tin properties
• Tool properties
• Toolbox properties
• Topology properties
• VPF Coverage properties
• VPF FeatureClass properties
• VPF Table properties
• Workspace properties

Working with Property sets

Some properties are members of a Property set. For example, the tolerances of a coverage or the connection properties of a workspace return as Property sets. Property sets have named properties that can be called from the property set. In the example below, the tolerances of a coverage (fuzzy, dangle, ticMatch, edit, nodeSnap, weed, grain, and snap) print to the standard output:

import arcpy

# Describe a coverage feature class
#
desc = arcpy.Describe("D:/St_Johns/covs/freshwater")

# Create a property set of coverage tolerances
#
covTols = desc.tolerances

# Print each coverage tolerance
#
print(covTols.fuzzy)
print(covTols.dangle)
print(covTols.ticMatch)
print(covTols.edit)
print(covTols.nodeSnap)
print(covTols.weed)
print(covTols.grain)
print(covTols.snap)

Property sets are typically used when the properties of the object being described vary. The connection properties (server, instance, database, user, and version) of an enterprise geodatabase workspace vary depending on the type of ArcSDE database that is being used, so it is well suited to a property set that has no predefined set of values.