https://youtu.be/ELbzAWIFXmkGraffiti is the oldest of all the Hip Hop elements. It goes back to the dawn of man.
it's a primal urge something that is ingrained into humans. For one they have wrote on walls as long as man has been around. You will also notice what's the first thing a small child does with markers?
while a lot of major cities have set aside areas where graffiti is not only legal but welcomed. In Wynwood a subdivision in Miami they hire international artists to keep all the walls covered year round and is referred to as the art district.
while many artists choose to remain anonymous and work under cover of night to illegally cover walls. Some even giving their lives in the process ( R.I.P. Ynot, Demz & Reffa) some artists such as Florida's Crook & Chrom gained notoriety by how large the scale and frequency of their work. Covering most of south and central Florida. For people not familiar with the area it's about 8 hours to drive.
some artists become so well known and switch to tattoos charging $200-$300 per hour for the art. A well known and respected artist in Miami that goes by the moniker Ahol SnifsGlue got into a legal battle with the clothing company American Eagle Outfitters. The ended up costing the company over $100,000 for counterfeiting the artists work in their catalogs and stores.
if you decide to take pictures of local graffiti in your area PLEASE BE CAREFUL! In many cities the act of photographing graffiti is illegal and you can be fined and even put in jail.