by Rupert Bainbridge, Northumbria University
Back in May I was lucky enough to get to go on some fieldwork to New Zealand, travelling to some pretty remote locations. Having done some similar fieldwork in the past one thing I didn’t want to do was cart around a laptop and charger with me as the journey out is quite long and the weight limit can be a bit restrictive if you have a lot of fieldkit. To this end I decided to take a tablet with me instead, granted it still needed a charger but it’s much lighter and less bulky to carry around.
I decided to have a look into how useful a tablet might be actually in the field rather than just in down time and came across an app called PDF Maps, many of you reading may have come across it and used it before. Personally I thought it was a great addition to the fieldwork arsenal and has some useful functions for the field researcher.
OK, so initially you obviously need to have an internet connection to load up maps, but one of the apps best features is that once you’re set up it can be used completely offline! The maps are stored on the device, not run from the internet.
When I’m talking about maps with this app, it’s really any piece of georeferenced material; satellite/aerial imagery, geology maps, topo maps, geomorph maps etc., so long as the files have been prepared correctly they’ll all work. There are a couple of methods for putting maps onto your tablet for the app to use.
- Download them using the in-app store. There are a number of different types of map available, in the store, I usually just click the ‘find maps’ option at the top and navigate to where I’m going to look at the range of things available in my destination. Luckily for me most of the topo maps in NZ are available for free and they’re listed in the app, so simply download and they’re ready to go. Alternatively there may be a small fee for downloading the maps, you can click on the available maps and see what price certain maps are.
- Prepare the maps yourself in ArcGIS. OK, so the maps you want may not be available through the app or they might be too expensive. Good news is that you can quickly and easily make them using ArcGIS, I haven’t tested this on QGIS mind you. I had a number of aerial images that I wanted to export and use in the field, some of them were already annotated and some blank, either is fine as the final product will just be a georeferenced PDF, so you can have some features already highlighted for when you’re in the field.
I’m not going to go through the whole process but there’s a great video for making the maps for the app (https://vimeo.com/79337719), they talk about the I-Pad in the video but I used the same process on an Android OS and it works a charm.
Finally once the maps are exported you need to transfer them to the tablet and load them into PDF Maps. I used Dropbox as an easy solution to this as there is an option within the app to directly import from a Dropbox app. PDF Maps lets you make folders and subfolders for organising anything you’re loading in (Figure 2) and will tell you if the georeferencing on the map isn’t working.
Using PDF Maps in the field
So once everything is loaded in and you’re finally at your fieldsite there are a couple of handy functions that can be used (Figure 3):
- Locate function: Like most phones these days, tablets usually have some sort of GPS function. A quick press of the locate button and you’ll have a pretty decent location for yourself in the field, I found this particularly useful for roughly locating myself on aerial imagery and topo maps when the scale of the maps weren’t quite as small as I would have liked.
- Placemarks: A placemarks function lets you put ‘pins’ on your imagery. The app just places the pin in the centre of the screen (using the bullseye symbol) so it can either be used in conjunction with the locate function and be placed on your location or you can pan around the map and place them where you like. Opening each placemark then lets you edit the description and name to whatever suits you. Photos can also be added to the placemarks, either directly from the device or at a later date from the device or other file sharing apps like Dropbox.
As a quick note, I haven’t tested the absolute accuracy of the positions given in the app against a handheld GPS or a dGPS. However when I was using this app I did try to get it to locate me in known locations and it was actually surprisingly accurate for the most part (around 5-10m) and even found me in some very remote locations when my handheld GPS wasn’t able to locate me. I suppose this matters depending upon how you plan to use the app.
- Measure Distance or Area: This does exactly what it says on the tin. Using your maps the app can estimate distance and areas (2D). It’s a bit clunky, but using the centre point you can create lines and polygons which then give a readout. I used this mostly for estimating some distances in the field to calculate walking times from place to place but it could of course be used for much smaller scale jobs.
- Jump to adjacent maps: You can also use the arrow buttons on the screen to jump to a menu which will show you nearby maps to the one you’re currently viewing. It’s a simple case of selecting the map you want to see. My NZ maps were labelled sequentially which helped when jumping from map to map.
All in all I found it a very easy app to navigate both in terms of loading maps and using it in the field to locate myself and log placemarks and descriptions of features. The maps were easy to prepare and load and the function buttons are really quite intuitive. Ultimately I found it quite useful for being able to take lots of imagery and maps into the field without carrying bundles of paper around and trying to keep everything dry.
For the fieldwork I did also buy a waterproof cover (Proporta Beachbuoy) for the tablet which worked very well in some pretty wet conditions!