You’ve planned the walk. You’ve got a grid reference from a guidebook or a friend’s recommendation. Now you need the map. But which one?
Ordnance Survey produces hundreds of maps covering Great Britain, all referenced by number, and the os map numbers list can look bewildering until you know how the system works. This guide explains the two main OS map series, how the numbering works, and the quickest way to find which map covers your area before you set off.
The Two OS Map Series You Need to Know
If you’re walking in the UK hills, you’ll be choosing between two OS map series. They cover the same ground at different scales. That makes a real difference when you’re navigating on the hill.
OS Explorer Maps (1:25,000)
Explorer maps are the walker’s map. At 1:25,000 scale, 4cm on the map equals 1km on the ground [MATT: please verify scale conversion]. You get field boundaries, rights of way, parking areas, and enough detail to navigate confidently in complex terrain. If you’re heading into hills or moorland, this is the map you want.
OS Landranger Maps (1:50,000)
Landranger maps cover a larger area at 1:50,000 scale, which means 2cm per km. They’re useful for planning at a bigger-picture level or travelling between walking areas, but they miss the fine detail you need for off-path navigation.
Many hill walkers carry both: a Landranger for an overview, an Explorer for the day on the hill.
Never Feel Lost Again: The Free UK Navigation & Safety Pack
Stop relying solely on a fragile phone battery. Download the exact tools a professional outdoor instructor uses to stay safe in the British hills.
Enter your email below to get instant access to:
- NEW: The Hike Planning & Safety Checklist: A comprehensive pre-walk checklist to ensure you never leave a critical item behind or rely purely on a smartphone.
- The Emergency Protocol Guide: A highly structured, zero panic system detailing exactly what to do if lost on Dartmoor/Scottish hills, including when and how to call Mountain Rescue.
- The OS Map & Navigation Cheat Sheet: A quick reference guide to decoding complex map symbols and plotting grid references when your mind goes blank.
- The Route Card Template: The exact, logic-driven framework I use to plan foolproof expeditions and identify safe escape routes before leaving the house.
- The Timing Crib Card: Never misjudge daylight again. Master the mathematics of measuring pacing distance and timings for steep ground.
Explorer vs Landranger: Which Should You Use?
For any walk involving hills, ridges, or remote terrain, use an OS Explorer. The extra detail is worth it. A Landranger won’t show you all field boundaries or footpaths, and that matters when you’re trying to confirm your position in poor visibility.
For road cycling, car touring, or big-picture route planning, Landranger does the job.
How the OS Map Numbering System Works
Each OS map gets a number. Explorer maps run from 1 to around 470. Landranger maps run from 1 to 204 [MATT: please verify both upper limits, these figures change as the series is updated]. The numbers weren’t assigned in a neat geographic sequence. They were added over time as the series expanded, so map 1 and map 2 are not necessarily neighbours on the ground.
[MEDIA: infographic | Diagram illustrating that OS map numbers are not geographically sequential — showing a few example map tiles and their numbers scattered around the UK | Helps reader understand why you can’t count to find your map | Alt: ‘Infographic showing non-sequential OS Explorer map numbers assigned to different regions of Great Britain’]
The OL Prefix: Outdoor Leisure Maps
Popular walking areas carry an OL (Outdoor Leisure) prefix rather than a plain number: OL1, OL2, OL3, and so on. These were originally a separate series covering the most-walked areas of England and Wales. When OS merged them into the Explorer range they kept their OL designations.
If you see OL on a map reference, you’re in well-trodden walking territory.
Why the Numbers Don’t Run in Order
Don’t try to find your area by counting up from 1. The numbers were assigned as maps were first published, not by location. The only reliable way to identify which map you need is to use the OS map finder tool or check the index printed on the back of any OS map.
How to Find Which OS Map Covers Your Area
Use the OS Map Finder Online
The quickest method is the Ordnance Survey website’s map finder. Enter a place name, postcode, or grid reference and it shows which Explorer and Landranger sheets cover that location. It will also flag if your area sits on two maps. Always check this before buying.
Find Your Map Number from a Guidebook
Most walking guidebooks list the OS map numbers on the route information page, Explorer and Landranger both. If you’ve downloaded a GPX route, the map number is usually in the route notes. This is the easiest shortcut when following a published route.
What If Your Walk Crosses Two Maps?
It happens more often than you’d expect, especially on long ridge walks or routes near map boundaries. If your route straddles two Explorer sheets, you have three options: buy both, use a digital OS Maps subscription that covers the whole country, or plan your route so the crossing point falls on easy ground where you can manage briefly without the detail.
Popular OS Explorer Map Numbers for Hill Walking Areas
For a full list, the OS website is the definitive reference. But here are the OL maps covering the most-walked areas in England, Wales, and Scotland:
[MEDIA: infographic | Clean reference table of popular OS Explorer OL map numbers and areas covered | Quick reference for walkers | Alt: ‘Reference table of OS Explorer Outdoor Leisure OL map numbers listing popular UK hill walking areas’]
- OL1 — The Peak District (Dark Peak)
- OL2 — Yorkshire Dales (South & West)
- OL3 — Dartmoor
- OL4 — The English Lakes (North West & North East) [MATT: please verify]
- OL5 — The English Lakes (North East)
- OL6 — The English Lakes (South West)
- OL7 — The English Lakes (South East)
- OL17 — Snowdon & the Conwy Valley
- OL18 — Harlech, Porthmadog & Bala
- OL23 — Cadair Idris & Llyn Tegid
- OL44 — Loch Lomond & The Trossachs
- OL57 — Brecon Beacons (East) [MATT: please verify OL57 covers this area]
For Scotland outside of OL44, the Explorer maps use plain numbers rather than OL prefixes. The OS website map finder will give you the exact sheet.
Paper, Laminated or Digital: Which Format to Buy?
Once you’ve found your map number, you need to decide which format suits you. A standard folded paper map is fine for most conditions. A laminated Active Map survives rain and repeated folding far better. Worth it for a map you’ll use regularly.
A digital OS Maps subscription gives you the whole country on your phone, useful for planning and as a backup reference on the day.
But paper is still your safest navigation tool on the hill. Phones fail. Batteries die. A laminated OS Explorer weighs almost nothing and doesn’t need charging. Carry both if you can.
Summary
The OS map numbering system looks random at first. Once you know the logic, it’s simple. Explorer maps at 1:25,000 are the right choice for hill walking. They give you the detail you need to navigate with confidence. Use the OS map finder to identify which sheet or sheets cover your area before you set off.
Reading an OS map for beginners covers grid references, contour lines, and map symbols in plain language.
Bondringo Mountain Navigation Course gives you everything you need to navigate confidently in the UK hills, from home, at your own pace.
OS Map Finder on the Ordnance Survey website. Search by place name, postcode, or grid reference.
Frequently Asked Questions
What is the difference between OS Explorer and OS Landranger maps?
OS Explorer maps are at 1:25,000 scale, meaning 4cm on the map equals 1km on the ground. They show field boundaries, rights of way, and fine terrain detail. OS Landranger maps are at 1:50,000 scale and cover a larger area with less detail. For hill walking, use an Explorer. Landranger is more useful for big-picture planning or road navigation between walking areas.
How do I find which OS map I need for a specific walk?
The quickest way is the OS Map Finder on the Ordnance Survey website. Enter a place name, postcode, or grid reference and it shows which Explorer and Landranger sheets cover your area, including whether your route crosses two maps. Most walking guidebooks also list the relevant OS map numbers on the route information page.
What does OL mean on an OS map?
OL stands for Outdoor Leisure, a prefix used for Explorer maps covering popular walking areas in England and Wales. They were originally a separate series and kept their OL designation when merged into the Explorer range. OL1 covers the Dark Peak, OL17 covers Snowdon and the Conwy Valley. If a map reference starts with OL, you’re in well-walked territory.
What if my walk crosses two OS map sheets?
It happens, especially on long ridge routes. Your options are: buy both sheets, use a digital OS Maps subscription that covers the whole country, or plan your route so the boundary crossing falls in straightforward terrain where brief loss of detail won’t matter. The OS Map Finder will flag if your location sits on two maps.
Is a laminated OS map worth it?
Yes, if it’s a map you’ll use more than once or twice. Laminated Active Maps survive rain, repeated folding, and rucksack life far better than standard paper. The cost difference is small. For a home reference map you rarely take out, standard paper is fine.
Can I use a phone instead of a paper OS map?
A digital OS Maps subscription is useful for planning and as a backup reference on the hill. But phones fail, batteries die, and screens become unreadable in bright sun or heavy rain. Paper is still the more reliable navigation tool. Carry both where possible. Make sure you know how to use the paper map if the phone goes down. That’s exactly what the Bondringo Mountain Navigation Course covers.
