Apple maps address searches are not great outside the US; most of the addresses I have in my contacts don’t work or are not accurate.

My workaround … add a URL to the contact with the GPS co-ordinates (I used google maps to find the co-ordinates), such as:

http://maps.apple.com/?f=q&q=53.359568,-6.25946

This URL will forward to google maps when used on a non-Apple device or browser.