Assuming "City" and "Value" are headers for separate columns, maybe A and B on row 1, then try this:
Right click on your sheet tab, left click on View Code, and paste the following procedure into the large white area that is the worksheet module. Press Alt+Q to return to the worksheet.
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column <> 2 Or Target.Cells.count > 1 Then Exit Sub
Dim SortRange As Range
Set SortRange = Range(("A1"), Cells(Rows.count, 2).End(xlUp))
SortRange.Sort Key1:=Range("B2"), Order1:=xlAscending, Header:=xlYes
When you enter a new number in colum B, the range will sort itself.