Such umbrellas are often used to provide shade to the complete swimming pool and in this instance the umbrella is permanently fixed set up since it is a very large umbrella measuring as much as 15 feet across. 

Similarly, a large square umbrella is often used when providing shade over lawn furniture or protecting the furniture from rain etc. Patio umbrellas which are found in patio backyards, spas and restaurants often can be found in the square shape. 

This shape allows the umbrellas to be placed in such a way that no sunlight gets through, as their edges could be packed together and thus they totally blocking the sun. Same could be the case with rectangular patio umbrellas which can be found in clusters to provide perfect shade.

Patios often use square umbrellas which match their theme and best garden umbrella in bdthe architecture of the patio, its square and rectangular backyards and roofs. These terrace umbrellas now can be found in plenty of variations; a few of the square umbrellas have offset bases and central poles which make them even a little off-balance as well.

 Consequently all of the square umbrellas which are of comparatively smaller sizes have to be fixed onto the floor to help keep them from falling down. Often these are produced from acryl which will keep the users protected from the harmful ramifications of the sun's UV rays. The fabric found in these square patio umbrellas blocks as much as 90% of the harmful UV rays.