The Classes for Creating Maps: An Overview

Views Maps provides a set of classes that you can use to read data from various cartographic data sources (files, databases, map servers, and so on), create map features, transform the features into Views graphic objects using renderers, and position them correctly onto an existing map.

• The IlvMapFeature class is the item class for map features. A map feature is an object that represents a cartographic data as it was read from its source file. It can be a segment of road, an aerial image, the summit of a hill, or a digital terrain model. A map feature holds three main information fields: geometry, the projection in which its geometry is expressed, and its attributes. If the map feature is a town, for example, its attributes can be its name and the number of inhabitants. A map feature is completely independent of the way it will be graphically represented in the application. Thus, a point marking the summit of a hill might very well be represented with graphic objects as diverse as a cross, a circle, or an icon. For more information about this class, see the section Feature Iterators.

• The IlvFeatureRenderer abstract class is used to transform map features into graphic objects that can be added to an IlvManager. A feature renderer lets you select the graphic representation to be associated with a given map feature and to reproject its geometry in the projection system of the target application, if necessary.

• The IlvMapFeatureIterator abstract class is the common interface for readers. All the classes implementing this abstract class can be used to read cartographic data, whatever the original format. For more information about this interface, see the section Feature Iterators. Views Maps provides a number of predefined readers that all implement this interface. These readers are described in detail in Predefined Readers.

• The IlvProjection class in the use package projection is the base class for a large number of predefined projection classes. Projections are introduced in Selecting a Target Projection. For a detailed presentation of projections, see Map Projections.

The following figure illustrates the process for loading cartographic data into Views:

Loading External Cartographic Data into Views

• The IlvMapLoader class in the package format carries out this entire process automatically for all the predefined readers supplied with Views Maps. For information about predefined readers, see Predefined Readers.