Mapinfo sql, Features and feature collections, Feature – Pitney Bowes MapXtreme User Manual
Page 186: Features, And feature collections
Chapter 8: Working with Data
Features and Feature Collections
MapXtreme v7.1
193
Developer Guide
MapInfo SQL
The MapInfo SQL Language allows you to add powerful analytical processing to your MapXtreme
application. MapXtreme exposes SQL processing to users via the MapInfo ADO.NET Data Provider
for accessing data (specifically the
object). Expressions are also used for labeling,
thematics, legends, AddColumns, Feature searching, and Selection processing.
MapInfo SQL is standardized based on SQL-3 Specification. For example, you will find that:
•
String constants are enclosed in single quotation marks
•
Identifiers may be enclosed in double quotation marks
•
Select has no relationship to the Selection
A complete reference including code examples for the MapInfo SQL language is provided in the
MapInfo SQL Reference, which you can view directly from Visual Studio’s Help system.
Features and Feature Collections
The Feature class object model in MapXtreme offers a non-SQL-based approach to access and
manipulate data. This section covers the Feature class and IFeatureCollection interface. A key task
in working with features is the ability to search for them using a query definition object.
Feature
Features are described by their geometry, style, data source, key and attributes. Typically a feature
is a row in a table. A feature’s geometry is a FeatureGeometry object. FeatureGeometries can cover
a given area (MultiPolygon), a location (Points, MultiPoints); and distance (MultiCurves,
LegacyArcs). Additional Geometry classes that derive from FeatureGeometry and are used for map
features are FeatureGeometryCollection and LegacyText. (Rectangle, rounded rectangle and ellipse
objects also derive from FeatureGeometry, but are used primarily for cosmetic display purposes.)
One of the main uses of computerized maps is to gather information about the features. In
MapXtreme features are returned in FeatureCollections by any of several methods, either created
from scratch using a schema, selected using selection tools or methods or by searching the Catalog
for those that meet a specific set of criteria.