Chap providing article about Los Angeles (4)
'chap' is the definition.
(a chap named alan)
'article about los angeles' is the wordplay.
'article' becomes 'an' (indefinite article).
'about' means one lot of letters goes inside another.
'los angeles' becomes 'la'.
'an' enclosing 'la' is 'ALAN'.
'providing' is the link.
(Other definitions for alan that I've seen before include "-- Turing, English computer scientist", "-- Bennett, playwright", "- Ayckbourn, English playwright", "- Bates, - Bennett", "Messrs Ladd and Dukes".)