Please, correct my poor english

These icons are shortcuts for Chart → Field of Vision. Here you can set the width/hight of the displayed field of vision of your active chart to a predefined value (in degrees of arc). A click on the last icon sets the FOV to 360°.

You can change the default settings for the fields of Vision by Setup → Chart, coordinates → Field of Vision.

Each icon set corresponding cardinal point as point of view for the chart. Same as Chart > View Horizon.
Last icon set local Zenith as point of view.