Depth of field increases with higher number of aperture

For a given format size, at moderate subject distances, DOF is approximately determined by the subject magnification and the lens f-number. For a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF; decreasing magnification increases DOF. For a given subject magnification, increasing the f-number (decreasing the aperture diameter) increases the DOF; decreasing f-number decreases DOF.

The higher the f number the higher the depth of field. Landscape photographers like a high depth of field. As there is not always much point in a landscape photo where some of the photo is blurred.
A good way to rember is that Ansel Adams tha great landscape photogrpaher created a club called f /64. This was a high f number with great depth of field with max definition.
By having a high f number you need a longer shutter speed.
He wanted a great pictures. Adams was an admirer of Alfred Stieglitz and Paul Strand.
Many lenses for small- and medium-format cameras include scales that indicate the DOF for a given focus distance and f-number; the 35 mm lens in the image above is typical. That lens includes distance scales in feet and meters; when a marked distance is set opposite the large white index mark, the focus is set to that distance. The DOF scale below the distance scales includes markings on either side of the index that correspond to f-numbers; when the lens is set to a given f-number, the DOF extends between the distances that align with the f-number markings.

Isle of Man Mansions
isle of man