Using Avenza Maps
An app that is available for Android and iOS devices that appears to do what we require for navigation, sampling purposes and marking out features is Avenza Maps (AM). I have no particular allegiance to AM, and if there is another app more suitable for our purposes, please let me know, it was the first reasonably well-known GPS app I tried that seemed to fit the requirements.
There are a number of functions in Avenza Maps that are useful for field work. A Placemark (waypoint) can be created at a desired location on a Map, either at the point you are currently at, or by moving the cross-hairs to the desired location on the Map first. One or more photos can be taken and associated with a given Placemark. Placemarks can be exported from your device and then displayed in Google Earth. Descriptions of a Placemark location can be entered (see example below).
The most useful functionality imo is the ability to use your own geotiff image as a background map, placing waypoints etc. on top as you move about in the field. Also handy is the ability to take photos and associate them with a given waypoint.
The app is ‘free’, however there are some limitations on the free version, the main one being a maximum of 3 maps loaded into the app at any one time, no biggy. There is a pricey annual subscription for the “Pro” version, I don’t think it is really required at this stage, but I did notice that it claims to be able to handle Shape files too.
After installing the free app from your relevant App Store, you will see that the “My Maps” screen is the main landing place. The first thing to do is to get some maps onto your device. In our case this will usually be an aerial photo in geotiff format.
How to get a Map onto your device
First thing is to save a geotiff physically to your device, some methods include connecting a data cable to your phone (I couldn’t seem to do this on iOS?) and transfer the geotiff using your phone’s file explorer tool. Another way is to email it to yourself as an attachment or link, or you could probably also transfer geotiffs from cloud-based storage as well.
Navigate to the “My Maps” screen.
On my phone (an Android Samsung S8) an orange “+” button is present in the lower right of the “My Maps” screen. If you tap it, it expands to give extra options including “Download or import a map”. Tap on this.
I think an offline map is going to be the most useful option in most cases, so that a mobile data connection is not required for it to all work in the field, especially the rugged west coast areas.
Tap on “From Storage Locations” and navigate to the folder you have saved some geotiffs locally on your device.
Select one, Avenza will then import the geotiff image, tiling it nicely as it does so. If you already have 3 maps loaded, you will have to remove an existing one first. This is OK, as it will still be in your folder if you need to shuffle it back again later.
The “My Maps” screen will now have your geotiff present in the list as a new map.
Load a Layer
Tap the “Layers” icon on the bottom of the screen.
Tap the floating orange Menu button near the bottom of your screen, and then select “Import Layers”
Tap on “From Storage Locations” and navigate to the folder that you have saved some layers to locally on your device. You may get a Warning dialog asking you to link your new layer to an existing Map. Do this – selecting a Map (already present in Avenza) that you wish to have as the background image to the layer you are about to load. This should import the kml file as a new layer in Avenza Maps, with it now appearing on your Layers screen, probably right at the bottom if you scroll down.
Now, when you are within a Map area according to the GPS on your phone, your location will be shown as a blue moving dot with a round uncertainty envelope surrounding it. Your linked layer should be shown, with any waypoints being visible. If you tap a waypoint, its name should appear.