You might try using a Lookup function.
In case you are not familiar with it:
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Go to Sheet2.
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Fill cells A1 through A4 with the list of suburbs.
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Fill cells B1 through B4 with the list of corresponding regions.
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Go to Sheet1
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In cell B1 type (without the quotes) “=IF(ISBLANK(A1), “”, LOOKUP(A1, Sheet2.$A$1:Sheet2.$A$4, Sheet2.$B$1:Sheet2.$B$4))”
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NOTE: The IF and ISBLANK parts are not necessary. They just make things look nicer. You could just type (again, without the quotes) “=LOOKUP(A1, Sheet2.$A$1:Sheet2.$A$4, Sheet2.$B$1:Sheet2.$B$4)”
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Copy cell B1 down however far you want it to go.
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Type a subdivision name into cell A1. Cell B1 should display the appropriate region listed on Sheet2.
If you add rows to Sheet2, you will need to update the formulas in column B on Sheet1.
I hope that helps.