Contents: Maps: Raster vs vector

What are raster and vector maps?
Traditional paper maps (raster)
Digital-only maps (vector)
Summary table: Raster vs vector

What are raster and vector maps?

Raster and vector are the techie terms used to describe the two types of offline maps commonly used with smartphones and GPS handhelds. Both can provide the topographic information we want to see outdoors but they behave quite differently to each other. It’s helpful to understand the pros and cons of the two map types when choosing navigation apps and maps.

Raster maps are usually government funded and commercial paper maps (like OS maps) converted for use on a phone or GPS handheld. Vector maps are purpose-built for electronic devices. Those made for consumer devices typically contain additional information, like extra paths, not shown on commercial mapping. Their clever design offers other advantages too.

GPS devices armed with both map types will be more useful than those only offering ‘paper’ maps.

Traditional ‘paper’ maps (raster)

This type of map will be familiar and easy to understand. Electronic copies of traditional paper maps. In my experience, Government funded and commercial map offerings are always of this type.

eg OS maps for the UK, Harvey Maps (UK), IGN France, Swisstopo, Spain’s CNIG, Kompass maps etc. They’re all available for smartphones and some will be available for GPS units. A map looks identical on a phone or handheld to the original paper version.

They behave just like a photo of the paper map. You can zoom in for a closer look or zoom out to fit more on the screen. Zoom in a long way and you’ll just start to see the pixels that make up the image. No extra information is revealed.

Zoom out too far and you can’t read the map because the details all get too small.  At that point you might need to switch to a different scale map. No surprises, exactly what you’d expect.

Digital-only maps (vector)

You might never have heard of vector mapping but you will almost certainly have used a vector map before. Although it’s wholly unsuitable for outdoor adventures Google Maps is an example of a vector street map made available to our web browsers. You have probably noticed how details appear and disappear depending on how zoomed in/out you are and the text always stays the same size. The map doesn’t have a fixed scale either, it’s continuously zoomable. These are all features of vector mapping.

Although it’s possible to print vector maps to paper, they are purpose-built for electronic devices and offer a flexibility that you don’t get with converted paper maps. So how are vector maps different to a traditional paper maps?

A converted paper map (raster) exists as an image. An app can’t show the map without, for example, the contours. They are an integral part of the image. You get the map image and that’s that.

A vector map exists not as a fixed image, but as a long list of separate descriptions of all the elements in the map. ie Roads, rivers, buildings, woods, contours, rocks etc. Some apps allow you to significantly customise what is shown and how it looks.

eg With OsmAnd the map can be ‘themed’ to be a simple road map, a detailed topographic map or a ‘skiers’ map with slopes coloured according to steepness.

A vector map’s appearance can be customised to suit the activity.

If you wanted to use the map as a driving map the right app/map combo can switch contours off and make the roads appear wider so they are more easily seen. A road could be made red or yellow depending on the app settings. Text size can be altered to suit your eyesight. In practise good apps will offer sensible customisations of vector mapping that can be tweaked by the user to suit the chosen activity. eg Driving, hiking, city wandering, mountain biking, etc

The Ordnance Survey explain in 3 minutes the difference between a raster map and a vector map.

Some of the best topographic vector maps, for countries all over the world, are available to download and use for free. No catch.

Vector maps often contain good paths and other details that are not marked on government-funded maps like the Ordnance Survey maps in the UK.

It doesn’t matter if you’re so zoomed-out that you’re looking at the overview of the entire country, or so zoomed-in that you can see phone boxes and benches on a pavement. Text and map features always remain readable and the image is always crystal clear.

A single vector map of a country does away with the need for different maps at different scales.

Vector maps can offer Google-Maps-like detail in town centres. In wilder terrain, features as small as individual rock buttresses and cairns may be marked and named where appropriate.

Vector maps are not limited by a fixed scale and can record small details absent from traditional paper maps.

A vector map only needs a small fraction of the storage of a traditional converted ‘paper’ map.

Permanently store whole countries on your phone or GPS device.

I have several vector maps of the UK on my GPS devices. They are either free or cheap and guarantee I’ll have good offline mapping wherever I go. No internet or phone signal is required to use them, and there’s no subscription to maintain. Give ‘em a whirl.

So, how are these great free maps possible? Our thanks must go to the ‘Wikipedia of mapping’, OpenStreetMap. OpenStreetMap (OSM) is a brilliant and widely used free resource. ‘OSM’ maps are now everywhere and behind many of the nav apps available. Learn more in Maps > OpenStreetMap.

Summary table: raster vs vector maps

Feature	Converted ‘paper’ maps (raster)	Vector maps
Cost	Expensive	Free or very cheap
Consistent coverage?	Usually excellent, but many paths are not mapped by the OS.	Variable. Can rival or better commercial mapping where there’s good internet connectivity eg In the UK and Europe.
Detail away from towns	Excellent. Paths, good crag detail with accurate contours and other topo features..	Good. Many paths are marked that are not on OS maps. Contours are less detailed and crag markings are basic, or even absent.
Detail in towns	Mostly building outlines.	Excellent. Street names, shop names, banks, food shops, cashpoints etc may be marked.
File size	Large (15GB for OS maps at 1:25k and 1:50k)	Much smaller (2GB for UK)
Zoom friendly	No, but good apps will switch between scales when zooming.	Yes. Always readable.
Routable	Online routing services sometimes provide snap-to-path plotting using ‘paper’ maps.	Some phone apps offer both online and offline snap-to-path plotting. ‘Routable’ Garmin maps snap-to-path offline too.
Can we edit the map?	No.	Yes. Any changes to OpenStreetMap will quickly propagate around the world.
Path reliability?	Beware ‘Public Rights of Way’ on OS maps. They may not exist on the ground.	Usually uncannily accurate but a few are ‘patchy’ at best on the ground.
Customise?	No. Simple ‘overlays’ may be offered to highlight cycle tracks or similar.	Sometimes. You may be able to choose what the map shows and how it looks.
Points of Interest?	Some apps may superimpose these over the map.	POIs may be built-into the map and link to useful information.