I've travelled to many western states hunting upland birds and have used mapping applications extensively for several years. My opinions:
OnX Hunt has great data. The base maps are good and the ownership data is tremendously useful. It all works well when you are online, either with LTE or with wifi. However, the off line map feature is awful. It is very difficult to select the data for download, the download process is horribly inefficient, and I've seen the saved data go strangely corrupt in the field. I still use it but would prefer an alternative.
Montana Hunting 2016 is far stronger - but is only available for Montana. I highly recommend it to anyone who wants to use public land or block management land in Montana.
There are other mapping apps with only forest service information but I've not tried that route. The private land ownership overlay is key to bird hunters.
I expect that apps will improve over time. Apps plus an iPad are definitely the way to go hunting public land in the western states.
1 week ago