# None Values or Missing Data

Suppose I have a feature "Pool Size" whose levels are: Big, Medium, Small.

Surely if a house doesn't have a pool it certainly won't have a value for "Pool Size".

Q1-For this particular instance/house, should I consider the value for "Pool Size" missing ('NA') or should I makeup a new category for 'Pool Size' dedicated to houses that do not have a pool size lets call it 'None' or 'NoSize'?

Q2-If I choose to makeup a new category for 'Pool Size' then my feature would become categorical instead of ordinal. Wouldn't that be a problem as I am essentially changing the nature of the variable?

If you are able to get this information, it would be good to include it into the dataset. Your proposal to add a value none to the size feature sounds okay, after all, no pool is still smaller than a small pool. However, if you want to keep the feature ordinal as it is, you could add a new binary feature has pool to indicate this information.