After you have formed a selection, it can be reduced by specifying a further query condition. In the previous chapter, we selected all parcels that could be affected by leakage from the underground gasoline storage tank at the gas station shown below. We also computed the total and average values of these properties but found that some of them have no assessment value. In this example, we will remove from the previous selection those properties without assessment values to obtain more meaningful statistics.

(288706, 740328), 1:500

 

 

 

 

 

Form a selection of parcels.

1. As explained in the previous chapter, create a buffer zone 50 metres from the gas station but excluding the gas station itself. Form a selection of parcels overlapping this zone.

NOTE If you have just finished the previous exercise, you would have formed the proper selection for this exercise.

2. Pick Data > Reselect ... from the DB Manager.

3. Select from the current selection those properties with current assessment values not equal to zero. The operator used is not like for "not equal to". A new selection will form and a report will be generated.

NOTE :  In the reselect command, retrieval is performed on the selected data list and not on the entire database.

4. Pick the Data > Statistics ... menu item to generate statistics for the selected parcels. You will notice that there are now only 15 parcels selected and the average value is higher than last time since we removed those with no assessment value.

5. Highlight the selected parcels