MapViewer - Key Concepts
Some fundamental concepts include:
- base map,
- and map.
A feature is an entity with spatial and non-spatial attributes such as cities, rivers and highways. A feature can be represented by a polygon, a line or a point.
Some features displayed on a map essentially provide a spatial context and the user is unlikely to want to click on them and have some action performed as a result. Streets, rivers, and forest may be such features.
Feature of Interest (FOI)
The user may want to interact with other features, such as store locations, postal code boundaries, or oil pipelines displayed on the map. These are called Features of Interest (FOIs).
Within the context of a MapViewer application, FOIs usually display the geographic extent or location of some business object such as customer or store location, sales territory, or delivery zone.
A style defines rendering properties for a feature. For example, if the feature is a polygon showing a county, then the style may define the fill color for the county or it may define a pie chart to be drawn over the county.
A theme is any collection of features that have a common set of attributes and a location. Typically, a theme is associated with a spatial geometry layer.
For example :
- A layer on the map displaying boundaries for US states would be considered a theme.
- A layer on the map displaying major US highways would also be considered a theme.
- Other types of themes include, but are not limited to, image themes which may be used to display satellite overlay or a relief map.
A basemap consists of one or more themes.
For instance, a base map may be composed of themes that show US state boundaries, county boundaries and markers for cities.
A map can have a basemap and a stack of themes rendered on top of each other in a window. A map has an associated coordinate system that all themes in the map must share.
A collection of features of interest is known as a FOI theme. It may be theme based or userdefined. An FOI theme based on a database query, or pre-defined theme in MapViewer parlance, is hence known as a themeBasedFOI. A user-defined FOI is created on the client side by the application. For example, application may create these FOIs from results of an Answers request or some other web service call.
Themes, maps, and styles, and other MapViewer data and metadata are always associated with a datasource. A datasource is essentially a database connection and is usually a container (OC4J) managed datasource.
Non-spatial data provider
While MapViewer renders spatial data some of the content rendered on a map consists of nonspatial data such as sales volume, crime incident type, or store size. Often this data may come from a datasource that has no geographic information (e.g. Longitude-Latitude of store location, or coordinates defining the extent of a sales region) but does have an identifier, such as a place name or location_id, that links it to a geographic entity. In MapViewer parlance this is known as a non-spatial data provider. Examples are :
- CSV files,
- results of an Answers request
- output as XML
- results of a SQL query that contains no geographic objects.