• Selection tools
• Selecting elements
• Introduction
• Selecting by point
• Selecting by rectangle
• Selecting by polygon
• Selecting by layer
• Selecting by attributes
• Inverting the selection
• Clearing selection

Selection tools

Selecting elements

SELECT ALL

This tool is enabled when one or more vector layers are active in the TOC. The tool selects all the geometries (features/elements) in the active vector layers.

• "Select all" tool enabled if there are active vector layers in the current View.
• "Select all" tool disabled when there are no active vector layers in the current View.

The tool is accessed via the menu:

• View -> Selection -> Select All

The tool is not available if the layer is being edited.

SELECT BY POLYLINE

This tool is enabled when there is at least one active vector layer in the TOC.

• "Select by polyline" tool enabled if there are active vector layers in the current View.
• "Select by polyline" tool disabled if there are no active vector layers in the current View.

This tool selects those geometries of the active layers that intersect the polyline defined by the user.

The tool can be accessed in two ways:

• Via the menu: View -> Selection -> Select by polyline
• Via the icon on the toolbar

With the tool selected, move the mouse over the View and enter a series of clicks to define the polyline. Double-click to end the polyline.

You can use any mouse button to define the points of the polyline, including the final point.

If another polyline is created while holding down the Ctrl key then the geometries thus selected are added to those already selected. If, while doing this, a previously selected geometry is selected again then it will be deselected.

SELECT BY CIRCLE

This tool is enabled when there are one or more active vector layers in the TOC.

This tool selects geometries (features) of the active layers that intersect the circular area defined by the user.

• "Select by circle" tool enabled if there are active vector layers in the current View.
• "Select by circle" tool disabled if there are no active vector layers in the current View.

The tool can be accessed in two ways:

• Via the menu: View -> Selection -> Select by circle
• Via the icon on the toolbar

In the View click the mouse at the centre of the circle and then move the mouse outwards to define the size of the circle. Click once to finish drawing the circle.

Another circle can be defined while holding down the Ctrl key to add new geometries to those already selected. Previously selected geometries selected again in this manner will be deselected.

SELECT BY BUFFER ZONE

This tool is enabled if there is at least one active vector layer in the TOC.

"Select by buffer zone" tool enabled if there are active vector layers in the current View and these layers have plane coordinates.

"Select by buffer zone" tool disabled if there are no active vector layers in the current View with plane coordinates.

This tool selects geometries of the active layers that intersect buffer zones around selected geometries.

The tool can be accessed in two ways:

• Via the menu: View -> Selection -> Select by buffer zone
• Via the icon on the toolbar

• Tool requirements
  • Vector layers must be active in the TOC
  • The selection does not apply to layers with geographical coordinates, only to layers with plane coordinates (e.g. UTM)
  • Geometries must be selected in at least one layer
• Configuration panel

When the tool is selected the following configuration panel is displayed:

• 1. Width: width of the buffer zone.
• 2. Unit: units of the buffer zone width.
• 3. Polygon: which side of the polygon to generate the buffer zone:
  • Outside: to the outside of the polygon.
  • Inside: to the inside of the polygon.
• 4. Line: for line layers the buffer zone will always be towards the outside.
• 5. Point: for point layers the buffer zone will always be towards the outside.
• 6. Multipoint: for multipoint layers the buffer zone will always be towards the outside.
• 7. Multi-layer selection: the selection will apply to all layers that meet the requirements.
• 8. Add buffer zone layers: when selected this option adds the generated buffer zone(s) to the View's TOC.

The new layers are named as follows:

• influence_areas_layername_num
• influence_areas -> prefix to identify this type of layer.
• layername -> name of the layer for which the buffer zone is calculated.
• num -> numerical suffix to identify each new buffer zone layer that is generated, automatically increased for each new zone generated from a single layer, starting from zero.

Example

Let's look at a typical example using the "Select by buffer zone" tool and four layers:

• A shape layer showing "Bird Special Protection Areas" of Castilla y León, obtained from the Ministry of Environment, symbolised with a filled "unique symbol" and with a transparency setting (zepa41):

http://www.mma.es/secciones/biodiversidad/banco_datos/info_disponible/zip/zepa41.zip/

• A shape layer showing "Sites of Community Importance" in Castilla y León, obtained from the Ministry of Environment, and using a unique values ​​symbology:

http://www.mma.es/secciones/biodiversidad/banco_datos/info_disponible/zip/lic41.zip/

• A shape layer shape showing the provinces of Castilla y León, using a unique values ​​symbology.
• A background WMS layer showing hydrographic information, topography, geology, road networks and administrative boundaries in Spain:

WMS Server: http://www.idee.es/wms/PNOA/PNOA/

Layer: PNOA

Style: Default

Format: image/png with transparency and SRS=23030

Now select the ​​bird special protection area called "Tierra de Campiñas", which belongs to Valladolid, Ávila and Salamanca. Also select the Site of Community Importance called "Montes Torozos y Páramos de Torquemada – Astudillo" in Valladolid.

Finally, we want to find the areas of type "lic" and "zepa" close to (up to 15 km) the selected areas so that, for example, they can be taken into account in a future second phase involving work to protect birds.

The following settings have been applied:

• The zepa41 and lic41 vector layers have been made active.
• Width is set at 15 kilometers.
• The two selected layers are polygon layers, and for this example the buffer zone is set to be outside the polygons.
• Indicate that the selection should be applied to each active layer (Multi-layer selection).
• Finally, add the generated buffer zones as new layers.

The result is shown in the following screenshot. The buffer zones can be turned off so that the selected areas can be seen.

• Details of the process

Click the "Show Details" button below the progress bar to show information on the steps that have been performed, including failures.

Sample output from the above process:

Selection is applied to each active layer that meets the requirements.

If the "Multi-layer selection" option is active, then for each buffer zone selections are applied to those layers that also meet the requirements.

If the projection of the layer is not the same as that of the View, an internal reprojection is performed in order to compute the buffer zones. The projection is later restored.

A shape layer is created (one for each active layer that meets the requirements) for storing the buffer zones. The location of each new layer is shown in the line beginning "Creating temporary file".

If the "Add buffer zone layers" option is selected, then the temporary layers are created and added to the TOC, symbolised with a unique symbol and with transparency.

If an active layer is not projected, then the applied selection is discarded.

If a failure occurs, the user is alerted and the selection process is terminated.

If the process is cancelled, the previous selection state in the affected layers is restored.

Introduction

You can select one or several elements or items by making either a graphic request or an alphanumeric request.

The selected data are shown in the view in the colour you have configured (by default this is yellow).

You can access the different ways of selecting elements by going to the tool bar or by going to the “View” menu and then to “Selection” as long as the layer you wish to work with has already been activated in the ToC.

Selecting by point

This is the basic selection method and consists of clicking on the element you wish to select.

Selecting by rectangle

This allows you to select the elements which are partly or wholly located inside a rectangle.

To define the rectangle, place the cursor point over the position you wish to start to draw the rectangle in, left click on the mouse and hold the button down until you have defined the area you wish to select.

Selecting by polygon

This allows you to select elements which are partly or wholly located inside a polygon.

To define this polygon, place the cursor in the part of the view you wish to draw the selection polygon in. Left click on the mouse in the view to add the polygon vertices.

When you have finished, double click on the mouse. All the elements which are located inside the polygon or which intersect with any of its sides will be selected.

Selecting by layer

You can access this tool by going to the “View” menu then to “Selection” and “Selection by layer”. It allows you to select elements in the active layer based on the selection made in another layer.

The options available using this tool are:

• 1.New set: This creates a new selection set.
• 2.Add to set: This creates a selection set based on the previous request and the current request.
• 3.Select from set: This creates a selection set from what has already been selected, the current selection request is extracted from the previous one.

An example of how to use this tool consists of selecting the cities and towns of the Valencian Region whose municipal boundaries are affected by flood risks.

We start with a shape file with the areas of the provinces in the Valencian Region which are subject to flood risks.

Then the layer corresponding to all the cities and towns in the Valencian Region is added. Pre-select the full flood risk layer.

We go to the “Selection by layer” tool. Use the “Intersect with” option in the first pull-down menu, “Select items from active layers that are:…”.

Use the “riesgo_inundación_25000_completo” option in the second pull-down menu “Selected items of a layer”.

We can now click on “New set” and the layer with the new selection will appear.

Selecting by attributes

You can access this tool using the following button:

gvSIG allows selections to be made using requests (filters). Selecting elements by attributes allows you to define exactly what you want to select, including several attributes, operators and calculations.

Requests can be made using logical operators, such as “equals” “more than” “different from”, etc.

If you press the “Filter” button in the tool bar, a dialogue window will appear to define your request.

1.Fields: Double click on the field you wish to add to your request from the “Fields” list in the layer.

2.Logical operators: These allow you to insert a logical expression into your request by clicking on them.

3.Values: This shows a list with the different values the selected field has. If you wish to add a value to the request, double click on it.

4.Request: This is the window which represents the request to be made. You can write here directly.

5.Selection buttons: These buttons make the request using:

New set (deletes any previous selections).

Add to set (adds the elements selected by the request to the existing elements).

Select from set (makes the request from the selected elements).

Inverting the selection

When you have made your selection, you can click on the following button in the tool bar

or you can go to the “View” menu then to “Select” and “Invert selection”

and invert the previous selection as shown below.

Clearing selection

If you click on this button, the selected element set will once again become empty. You can also access this option by going to the “Layer” menu then to “Clear selection”.