Why is the map sometimes incorrect?

Deliveries takes the location given from the shipping company and asks Apple's mapping service where it is. Sometimes the mapping service will make the wrong guess at where that location is, especially if it's not specific enough (for example if the shipping company doesn't specify the country). You can drag the pin to the correct location, and it will remember any corrections you make for the future. Just tap and hold the pin, then move it to the correct place.