The most likely reason for a cat spraying is to mark territory.
There is a distinct difference between a cat that sprays and a cat urinating outside the litter box. For information and advice about litter box problems please see this page - Cat Behavior
Spraying (urine marking) is the most usual way in which cats mark their territory.
But scratching, rubbing themselves against objects and not burying their feces are other methods of marking.
The cat will back up to the vertical object that he or she wants to mark - a wall, your sofa, your drapes etc.
The tail will be held up high, and will usually be quivering, often he will tread the ground with his paws.
He will then spray a fine stream of foul smelling urine at just the right height for any other cat to smell it.
Both cats that are kept indoors all of the time and cats that are allowed outdoors will spray inside the home.
Not all cats will do this of course, but when it happens it's a big problem for owners.
A cat will urine mark not only to communicate to other cats but to label its territory with its own smell to boost its self esteem and confidence.
Spraying urine in the home can be an indication that your pet is feeling distressed and needs to feel more secure by surrounding itself by its own fragrance.
Un-neutered and un-spayed cats are by far the most likely to spray.
With the unaltered cat, urine marking will not only signal the cat's occupancy but also its status. Unaltered male cat spraying is triggered by hormonal changes when Tom reaches sexual maturity.
Female cats in heat have high levels of oestrogen in their urine. This is mixed with secretions from their anal glands and results in a very strongly smelling spray that is attractive to Tomcats.
A neutered or spayed cat will also sometimes spray urine indoors, although this is less likely than with an unaltered cat.
The most likely reason for an altered cat spaying is stress.
The sight of a neighborhood cat outside the window may trigger feelings of insecurity. Another cat's scent upon your clothing could result in your cat feeling threatened.
The introduction of another cat into the home can be very stressful for your existing feline friend, and conversely of course the loss of a companion cat will be upsetting for kitty.
Strangers in the home, a new baby, a new partner, can all serve to make your cat anxious and the response could be urine spraying.
Even new items of furniture, rearranging furniture, a change of household routine or the redecoration of a room, can all cause your cat upset.
A home with a great many cats trying to establish territory in limited space will likely result in spraying indoors.
Cat doors are a boon if you have an indoor-outdoor cat. But sometimes the presence of a bullying neighborhood cat will make your kitty insecure.
Your cat cottons on to the fact that if he can get into the house through the cat flap then so can the bully.
So, to signal to the cat world that the house is his territory your cat sprays the cat flap.
Blocking up the flap should cure the spraying, but, of course, it will mean that you’ll need to let the cat in yourself.
If this is your problem you may find an electronic pet door solves it.
If you in any way suspect that your cat spraying could be a medical problem consult your veterinarian.
If no medical reasons are found for the behavior, medication may be prescribed.
Medication can reduce your cat’s anxiety and need for spraying.
Could a Feliway Diffuser possibly help you to end your cat's urine marking?
Do you have an aggressive cat?
There are many reasons that your cat may display cat aggression. If you can discover the cause of your cat's aggressive behavior then you can help calm your pet.