Depth of Field in Photography

Deep Depth of Field, this results in an image that is reasonably sharp from the foreground to the background. Using a narrow aperture, such as f/11, is ideal to keep photographs of landscapes or groups in focus throughout.

A factor to consider when working with depth of field is your distance from the subject. The farther you are from the subject you are focusing on the greater the depth of field in your photograph. For example, if you stand in your front yard to take a photo of tree a block away, it has a deep depth of field with the tree, background, and foreground all in relatively sharp focus. If you stand in the same spot and take a picture of your dog that is standing just several feet
away, your dog is in focus, but that tree a block away is just a blur of color.

Small f-number means wider aperature opening

A small f-stop such as f/2.8, for example, opens the lens so more light reaches the sensor. If you have a wide aperture (opening), the amount of time the shutter needs to stay open to let light into the camera decreases.
Big f-number may be used in landscape photography as it provides depth of field.
Remember it is a reciprocal relation, big number means small opening, small number means big opening.
With big opening you can photograph more details.