how do I add an apartment number to a contact

Just add the apartment number after the address, separated by a comma. Here's a Contacts card like that, clicking on the Maps icon that appears to the right of the address (not shown in the screenshot) opens that address in Apple Maps just fine.

That same format works for mail and parcel delivery, too.

roonz wrote:

a member of my family has just moved into an apartment which has its own number on the door, so if I want to post something I need to enable the apartment number on one line, and the number of the apartment block on the second line, then the city on the third line and finally the postcode on the fourth, How do I get contacts to allow me to add these separate fields to my preferences, it appears that I am only allowed to fill in the prescribed data, so will have to have the apartment number and street number and name all on the same line, which means that

Apple Maps does not recognise the address

just add it to the street address line:

streetaddress#aptnumber......(?)

unit#

streetaddress#unitnumber

Apple maps is not going to drill down to an apt number no matter what you do. Street address—yes.

you can submit your Apple Feedback here: Product Feedback - Apple

right ....

I would not make this overly complicated as some algebraic equation.

For example I have all packages shipped: UPS /FedEX /DHL to my USPS P.O.Box

it is simply:

StreetAddressOfTheUSPS #P.O.BoxNumberFollowsHere

sometimes it will automatically get changed to

StreetAddressOfTheUSPS Unit P.O.BoxNumberFollowsHere

The take home lesson is— you do not need to be pedantic here.

There are more than one way to seamlessly handle variations in the address.

you can take the same example address from above and google maps will render it differently

120 Mathewson Street, Apt 21

Providence RI 02903:

see https://www.google.com/maps/

Here is what USPS expects: https://pe.usps.com/text/pub28/pub28c2_003.htm