Map book has bit of Texas torn out unfortunately (4)
I believe the answer is:
alas
'unfortunately' is the definition.
('alas' is used to express regret)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for alas that I've seen before include "Cry of woe" , "Regretfully!" , "By bad luck" , "Unhappily" , "What a shame!" .)