If your device’s Location Services is disabled, your location fix will not be as accurate. Also, iPod and Wi-Fi iPad devices cannot use cell towers to fix a location so they will be less accurate.

If you create a new saved location and its location is not as accurate  as you’d like, you can refine your saved location’s pinpoint. Before you tap Accept, drag the pin closer to the area where you would like to  receive alerts (tap and hold down the pin before dragging; it may help  to zoom in the map for more detail before dragging the pin), then tap Accept.