Having seen an air ambulance attend an incident yesterday made me pay attention to a blue crt sign at North Grove lock

E 507 985 N 201 235

Where is this from as its not its Long Lat reference

It's the OS grid reference. Cheers Graham

9 minutes ago, Tonka said:

Having seen an air ambulance attend an incident yesterday made me pay attention to a blue crt sign at North Grove lock

E 507 985 N 201 235

Where is this from as its not its Long Lat reference

It is lat-long (but not the normal degrees minutes and seconds) but (I believe) it may be the "DD" (Decimal Degrees") system using "World Geodetic System 84"

It is one of the format options on my hiking GPS system - if it is, it is not widely used in the UK.

A quick AI search :

Here are some key points about Decimal Degrees:

• Format: DD is a decimal representation of latitude and longitude, where each degree is expressed as a decimal fraction. For example, a location might be represented as 37.5665°N 123.4567°W.

• Usage: DD is commonly used in GPS devices, GIS software, and mapping applications. It allows for easy conversion between different coordinate formats and provides a consistent way to represent locations on a map.

• Precision: The precision of DD coordinates can vary based on the number of decimal places used. For example, four decimal places are usually sufficient for most locations, while five or six decimal places may be needed for more precise measurements.

• Conversion: DD can be converted to other formats like DMS (Degrees, Minutes, Seconds) and DDM (Degrees, Decimal Minutes). This conversion is essential for compatibility with various mapping and navigation systems.

Edited October 2Oct 2 by Alan de Enfield

7 minutes ago, Alan de Enfield said:

It is lat-long (but not the normal degrees minutes and seconds) but (I believe) it may be the "DD" (Decimal Degrees") system using "World Geodetic System 84"

It is one of the format options on my hiking GPS system - if it is, it is not widely used in the UK.

A quick AI search :

Here are some key points about Decimal Degrees:

• Format: DD is a decimal representation of latitude and longitude, where each degree is expressed as a decimal fraction. For example, a location might be represented as 37.5665°N 123.4567°W.

• Usage: DD is commonly used in GPS devices, GIS software, and mapping applications. It allows for easy conversion between different coordinate formats and provides a consistent way to represent locations on a map.

• Precision: The precision of DD coordinates can vary based on the number of decimal places used. For example, four decimal places are usually sufficient for most locations, while five or six decimal places may be needed for more precise measurements.

• Conversion: DD can be converted to other formats like DMS (Degrees, Minutes, Seconds) and DDM (Degrees, Decimal Minutes). This conversion is essential for compatibility with various mapping and navigation systems.

7 minutes ago, Alan de Enfield said:

It is lat-long (but not the normal degrees minutes and seconds) but (I believe) it may be the "DD" (Decimal Degrees") system using "World Geodetic System 84"

It is one of the format options on my hiking GPS system - if it is, it is not widely used in the UK.

A quick AI search :

Here are some key points about Decimal Degrees:

• Format: DD is a decimal representation of latitude and longitude, where each degree is expressed as a decimal fraction. For example, a location might be represented as 37.5665°N 123.4567°W.

• Usage: DD is commonly used in GPS devices, GIS software, and mapping applications. It allows for easy conversion between different coordinate formats and provides a consistent way to represent locations on a map.

• Precision: The precision of DD coordinates can vary based on the number of decimal places used. For example, four decimal places are usually sufficient for most locations, while five or six decimal places may be needed for more precise measurements.

• Conversion: DD can be converted to other formats like DMS (Degrees, Minutes, Seconds) and DDM (Degrees, Decimal Minutes). This conversion is essential for compatibility with various mapping and navigation systems.

It can't be lat long as the lock is not east of Greenwich

15 minutes ago, Graham and Jo said:

It's the OS grid reference. Cheers Graham

No it isn't. The OS Grid reference for North Grove Lock is TL 07982 01233

Edited to say that Gumpy's more accurate version (below) is only a few metres different

Edited October 2Oct 2 by Mac of Cygnet

Google says

E 507 985 N 201 235

The coordinates E 507985, N 201235 represent a specific location point using the Ordnance Survey National Grid (OSGB36) system for Great Britain.

Converted into the standard alphanumeric format, this point corresponds to the 10-figure grid reference TL 07985 01235. This location is situated in Hertfordshire, England, just north of Watford.

Coordinates Summary

• Grid Square: TL

• Easting: 507985

• Northing: 201235

• Full Alphanumeric Reference: TL 07985 01235

It does indeed relate to the lock just south of the M25

4 minutes ago, Mac of Cygnet said:

No it isn't. The OS Grid reference for North Grove Lock is TL 07982 01233

It could well be the location of the sign rather than the actual lock 🫣

So where is it based from

7 minutes ago, GUMPY said:

Google says

E 507 985 N 201 235

The coordinates E 507985, N 201235 represent a specific location point using the Ordnance Survey National Grid (OSGB36) system for Great Britain.

Converted into the standard alphanumeric format, this point corresponds to the 10-figure grid reference TL 07985 01235. This location is situated in Hertfordshire, England, just north of Watford.

Coordinates Summary

• Grid Square: TL

• Easting: 507985

• Northing: 201235

• Full Alphanumeric Reference: TL 07985 01235

It does indeed relate to the lock just south of the M25

It could well be the location of the sign rather than the actual lock 🫣

2 minutes ago, Tonka said:

So where is it based from

In the dim distant past I could have answered that but I can't now😱

I used to use that system in my radio ham days I lived in SP54 however that was over 30 years ago and memory fades.

Ask Google that's how I got the answer.

https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid

Edited October 2Oct 2 by GUMPY

I am surprised at the confusion here. Didn't all of us learn how to read and create OS grid references in school geography lessons?

Just now, David Mack said:

I am surprised at the confusion here. Didn't all of us learn how to read and create OS grid references in school geography lessons?

60+ years ago.

No confusion here, just lack of memory.

2 minutes ago, David Mack said:

I am surprised at the confusion here. Didn't all of us learn how to read and create OS grid references in school geography lessons?

Yes, but just the 6 figure references (to 100 metres) The 10 figure reference quoted is to one metre accuracy!

Edited October 2Oct 2 by Mac of Cygnet

5 minutes ago, David Mack said:

I am surprised at the confusion here. Didn't all of us learn how to read and create OS grid references in school geography lessons?

Yes used them a lot in the scouts but you all have use the same map

5 minutes ago, Mac of Cygnet said:

Yes, but just the 6 figure references (to 100 metres) The 12 figure reference quoted is to 10 cm accuracy!

100m accuracy is enough to locate almost any lock.

Arguing about the sign post diameter is really rather pointless!

5 minutes ago, Tonka said:

Yes used them a lot in the scouts but you all have use the same map

Nope. Any map using OS grid will do. And before the days of online mapping, all the paper maps available to scouts would have had OS grid. They also had instructions in the margin on how to use grid references.

28 minutes ago, Tonka said:

So where is it based from

Off the SW coast, west of the Scillies, IIRC

6 minutes ago, Mac of Cygnet said:

Off the SW coast, west of the Scillies, IIRC

Yup. A spot south and west of the whole British mainland, so that all the eastings and nothings are positive.

22 minutes ago, David Mack said:

I am surprised at the confusion here. Didn't all of us learn how to read and create OS grid references in school geography lessons?

I dont think so, I did higher Geography, but I think I did grid references when I went on a winter walking weekend, we had to use a map and compass,

Edited October 2Oct 2 by LadyG

2 hours ago, GUMPY said:

my radio ham days

2 hours ago, GUMPY said:

Hallo from G3LCR

1 minute ago, Alan de Enfield said:

Hallo from G3LCR

G6LOH Not used it for well over 30 years🫣

1 hour ago, David Mack said:

Yup. A spot south and west of the whole British mainland, so that all the eastings and nothings are positive.

Not quite. Grid references apply not just to the mainland, but to all the offshore islands as well, including the Outer Hebrides some of which are west of the Scillies (but not of the SV square in which the Scillies are situated). Eastings and Northings in normal use take their origin from the SW corner of the two letter 100km square in which they are situated.

54 minutes ago, Mac of Cygnet said:

Not quite. Grid references apply not just to the mainland, but to all the offshore islands as well, including the Outer Hebrides some of which are west of the Scillies (but not of the SV square in which the Scillies are situated). Eastings and Northings in normal use take their origin from the SW corner of the two letter 100km square in which they are situated.

OK. Mainland was the wrong word. I meant Great Britain, since Northen Ireland uses a different grid, shared with the Republic (although it looks as if most if not all of NI lies within the area covered by OS NG).

I’ve done a job in the last couple of years where the organisation had created their own latitude and longitude system based on a specific point and aligned to something else other than north. To add to confusion the datum wasn’t at 0,0.

Working how that all worked was fun when the origin and alignment wasn’t available 😀

Used OS MR's recently on a car rally.

On 02/10/2026 at 15:28, David Mack said:

I am surprised at the confusion here. Didn't all of us learn how to read and create OS grid references in school geography lessons?

To be honest I have used maps my entire working life so its difficult to recall the beginning.

Do you really think most people remember something they were taught as a teenager if they have not used it in the last several decades ?

What three words is easier

6 minutes ago, MIKE P said:

What three words is easier

Not when the grid reference is on the sign