The separation of areas may require entities such as hedges and fences that are at eye level or slightly above, in order to provide visual separation.  On the other hand it is often necessary to separate areas simply by changing the surface treatment. 

A photograph showing hedges used to separate pa planting area and pathways.

Once the locations of the areas that you want to separate have been identified then organise your thoughts on paper.  Separation is often needed because of the change in the activities planned for adjacent areas.  Adjacent spaces can be defined by a change in elevation or by a change of materials used on the ground surface.  Planters or hedging can also be used as effective space dividers.

Certain areas of the garden may need to be completely hidden.  This may be to provide privacy or to hide unsightly areas or views.  The height for a screen will depend on the location of the object, view or other entity to be hidden.  Place your screen as near to the area to be hidden as you possibly can.  Many people use plant materials to provide a cost effective screen that will be effective and also provide some aesthetic interest.  They can however take up a lot of space and take time to grow.  

Fences occupy less space and provide an instant screen.  If you have made the decision to screen something, say a cooling system or oil tank, do at all costs avoid the temptation to use something like a trelliswork or other transparent screen.  The theory goes that plant will grow on the trellis and hide the oil tank.  This is rarely successful, resulting in the measure actually drawing more attention to the oil tank than if it were left in plain view.  Instead use something like a closed board,  or a board on board fence that efficiently blocks the view from the time it is installed.

It is possible to construct a combination fence and hedge by growing ivy or a selected vine on a simple galvanised or plastic coated wire fence that has been engineered for this purpose.  This gives you the advantage of having a hedge which is low maintenance, combined with the advantage of a fence which take up very little ground space.  It is best however to ensure that the plants are fully established on the fence before you install it.

Your budget and the available space will help you to make the decision about how you handle divisions in your garden.