Tick the check box in the column header, or press CTRL+A with the grid selected:

Zoom out so that all of the data is visible by clicking the Zoom Extents button on the map control toolbar, or in the contextual menu:

Hold down the SHIFT key.

Click the upper-left corner of the map control using the left mouse button.

Drag the selection tool to the lower-right corner of the map control using the mouse:

 Release the left mouse button to complete the selection:

Hold down the CTRL key.

Click on the map item or data item that you want to add or remove from the selection:

Change the selection in the check box adjacent to the data item that you want to add or remove from the selection:

Untick the check box in the column header, or click a row header:

Click any map area that does not contain a map item: