Spain seems to have given its vertical public spaces (of about twice human height) completely to practitioners of graffiti. There does not seem to be a single space left unmarked and unsigned. Any road, even slightly off the tourist track will have these profuse expressions of hombres at large. Although we did see some graffiti on vertical surfaces of such height that would have required rappelling skills!
Many are artistic in the fashion of the Miros of the spray can, although most are (probably) gang related territorial markers. The most vibrant and colorful graffiti that we saw was on one bank of the Guadalaquir leading up to the Alamillo Bridge in Seville.
Techniques also vary- a new form used stencils- leading to some fine work, and also work that could be replicated quickly, challenging the one off aura of larger, elaborately sprayed neighbors. A lovely one was in English that said 'Lost your (image of a) button'.
What makes graffiti a truly citizens art in Spain is the possibility of protest. Since every wall is fair game, exhortations/protestations indicate the contemporary climate. There are CCTVs everywhere and official indications to that effect. That has not stopped, probably encouraged a large graffito: 'Videosurveillance NON!' Others we saw said 'Securidad Muerte!' 'Free Catalonia' and my personal favorite- 'Errata, Ergo Sum'.