### TerraView Main Concepts

This new version of TerraView introduces some new concepts. It is important for the new user to have knowledge of these concepts, making it easier to adapt. Some of these concepts are:

#### Project

The project is a physical file that defines the workspace of a user. All layers created by a user are serialized in this file. Importantly, the data are not stored in the project file, but just a link to where the data sources are located.

#### Data Sources

The TerraView supports different data sources such as:

- Databases: PostGIS, Microsoft Access, SQLite

- Files: Files can either be vector files as raster files. To support these data types, libraries GDAL / OGR are used.

#### Layers

Layers are the representation of the data sets in TerraView. Initially there are some types of layers:

- DataSetLayer: This is the most common type of layer. Layers of this type have one data set that belongs to a data source.

- FolderLayer: This type of layer is used to facilitate the organization of layers in the Layer Explorer, allowing the grouping of layers.

- QueryLayer: This type of layer is used to create a subset of a DataSetLayer. For example, when a restriction clause over a dataset is defined, it generates a new dataset that is represented by this type of layer.

- TabularLayer: This type of layer is used to show a dataset represented in textual files with well-defined format such as CSV, or even binary files of type DBF. These files may or may not have geometric representations.

#### Layer Explorer

This component uses a tree structure to represent the layers contained in a project. A context menu is provided for quick access operations that are relevant to each type of layer or sub element of this layer.

#### Data Table

This component is a table used to represent the textual data associated with each layer. Context menus are also provided to access the relevant operations.

#### Map Display

The map display is the area to be used to render the selected layer in the layer explorer. This component defines a geographical reference system to be followed by all layers to be drawn in this component.

#### Style

The style defines how a data set should be rendered in the Map Display. For each type of geometric representation exists a kind of style to set it. A style is defined by a set of rules and the rules are composed of sets of symbolizers.

- Rules: It is possible to define a set of rules within a style, allowing different parts of the dataset to have different visual. The rule is a filter to be applied to the data set.

- Symbolizers: Structure that defines how an object should be rendered. Attributes such as fill color, opacity and others are defined in this element. A symbolizer can also be represented by an image file or well-known mark.

#### Style Explorer

Displays the style associated with a layer. This component is possible to add, remove or modify the symbols that make up the style. A property browser displays all attributes of a selected symbol, simply allowing its modification.

#### SRS / SRID

SRS stands for Spatial Reference Systems and SRID defines an identifier of a spatial reference. To correctly render a DataSetLayer in a Map Display it is necessary to have consistent SRIDs (projections) for both the Map and the Layer.

#### Plugins

Plugins are modules of TerraView that can easily be associated with or removed from the application. An example of these plugins are the drivers that support different data sources.