Map Scales.

[Paul_C]

I have a copy of a map that is in 1:1250 scale. The building that I am trying to build measures at 64 cm on that map so can somebody tell me the length of the real building please? I've found some info online that says 1cm equals 12.5 metres so I've come up with a figure of 1066 mm for the model (1/76 scale). Am I right or I am I barking up the wrong tree?

 

Paul.  

[petethemole]

1250 x 64 = 80000/76 = 1052.6cm.

[DGO]

Thats a big building 64cm equals  800M long in real life = 10.52M at 1:76 or did you mean 64 mm ? That would be an 80M long building in real life or 1052.6mm at 1:76 still large but reasonable for a railway building on a layout

 

[Paul_C]

Hi DGO,

 

😆😄🤣. Okay, now that I've picked myself up off the floor and stopped laughing we can start again. Yes, you're perfectly correct, I've just remeasured the map and it is 64mm so 6.4cm. I have this afternoon been working on the front-end section and I know that is correct as it is 1cm wide so 12.5 metres life size so converted into 4mm scale it is 162mm. I've spent some time this afternoon getting the roof pitch right and I think have got it pretty close.

 

So, if you would, can you please post what you think is the correct length please. Thank you.

 

Paul.

[Paul_C]

Many thanks to you also Pete, I initially came with 266ft as the length of the real building which transposed into 1064 mm.

 

Paul.

[Paul_C]

Following the response I had to my post I have gone for 1054mm as this was the figure suggested by the majority (I had personal messages as well) so I will now proceed and build the main shell. I've also found a lot of good accessories as well for the detailing.

 

Paul.

[Dungrange]

On 11/11/2022 at 09:10, Paul_C said:

I have a copy of a map that is in 1:1250 scale. The building that I am trying to build measures at 64 cm on that map so can somebody tell me the length of the real building please? I've found some info online that says 1cm equals 12.5 metres so I've come up with a figure of 1066 mm for the model (1/76 scale). Am I right or I am I barking up the wrong tree?

 

A map scale gives you the relationship between the measurement on the plan and the equivalent measurement in reality.  1:1250 means that the real building is 1,250 times larger than the dimension that you measure on the plan.

 

Therefore, if a building dimension scales as 64 mm on the plan, then it is 64 * 1,250 = 80,000 mm in real life (ie 80 m)

 

You are modelling in a scale of 1:76 or 1:76.2 (which is what 4mm scale actually is), so you need to follow the same process in reverse.  That therefore means that you divide the dimension in real life (80,000 mm) by the model railway scale, so we have either 80,000 / 76 = 1,053 mm or 80,000 / 76.2 = 1,050 mm.  Does that 3mm difference matter?  No, because we don't know how accurate your measurement of 64 mm is.  If in reality, the map measurement is, say, 64.1 mm, then the real dimension would become 80,125 mm, which when reduced to 00 would become either 1,054 mm (at 1:76) or 1,052 mm (at 1:76.2).  As long as you are selecting a measurement that is around 1.05 m, it should be good enough, so go with your 1054 mm.

[Paul_C]

A brilliant reply to my original question, thank you very much. As you say a few mil doesn't make much odds and your very accurate and detailed explanation just gives me further confidence in the stats that I've already received. 👍

 

I am actually on way over to my place of work as they have bench drills and cutting machines so I'm going to cut everything to size today, with this in mind your response has come at a very convenient moment 😃, thanks.

 

Paul.

[melmerby]

Another thing to bear in mind that the measurements on old maps aren't always that precise anyway.

All done by hand & eye with those linen tape measures and suchlike.

 

Modern maps derived from satellite images are much more accurate.

[monkeysarefun]

On 19/11/2022 at 00:17, melmerby said:

Another thing to bear in mind that the measurements on old maps aren't always that precise anyway.

All done by hand & eye with those linen tape measures and suchlike.

 

Modern maps derived from satellite images are much more accurate.

 

For still-existing` buildings the "Measure Distance" option on the menu that comes up when you right-click when in Google Maps satellite layer  is notably accurate also. Previous tests Ive done with it give the dimensions of my boundary fences accurate to within cm (allowable due to the slight fuzziness of the satellite image when zoomed in), and the length of my  ute parked in the driveway is an indicated 4.95m  - pretty close to the actual 4.894m, again allowing for the fuzziness 

Edited November 19, 2022 by monkeysarefun

[ikcdab]

On 18/11/2022 at 13:17, melmerby said:

Another thing to bear in mind that the measurements on old maps aren't always that precise anyway.

All done by hand & eye with those linen tape measures and suchlike.

 

Modern maps derived from satellite images are much more accurate.

I will speak up for our surveying forefathers! They did know what they were doing and used steel tapes for vital dimensions, not linen ones. Also they used lots of error trapping, so traverses were closed off and theolodolite levelling was also closed back to eliminate errors. I would say that the results they achieved were just as good as modern satellite images, its just that they took longer to do it, used more equipment and things could be missed. But what they did find and measure was done accurately and precisely. 

[Nick C]

On 21/11/2022 at 19:36, ikcdab said:

I will speak up for our surveying forefathers! They did know what they were doing and used steel tapes for vital dimensions, not linen ones. Also they used lots of error trapping, so traverses were closed off and theolodolite levelling was also closed back to eliminate errors. I would say that the results they achieved were just as good as modern satellite images, its just that they took longer to do it, used more equipment and things could be missed. But what they did find and measure was done accurately and precisely. 

Even if the map is perfectly accurate, there's still the thickness of the lines to take into account, and the accuracy of the measuring equipment you're using - Standard principle is 'half the smallest scale division', so if you are using a ruler marked to 1/2mm, then that 64mm could be 1/4mm out - conveniently, about a foot either way to scale...

[ikcdab]

2 hours ago, Nick C said:

Even if the map is perfectly accurate, there's still the thickness of the lines to take into account, and the accuracy of the measuring equipment you're using - Standard principle is 'half the smallest scale division', so if you are using a ruler marked to 1/2mm, then that 64mm could be 1/4mm out - conveniently, about a foot either way to scale...

Quite right.  I was a cartographer for 35 years and with a sharpened 9h pencil, the best we could plot by hand to was 0.2mm. That was only possible on drawing film such as Ozatex or Permatrace.  On paper, no hope and the 9H just tore the paper anyway!

[melmerby]

On 21/11/2022 at 19:36, ikcdab said:

I will speak up for our surveying forefathers! They did know what they were doing and used steel tapes for vital dimensions, not linen ones. Also they used lots of error trapping, so traverses were closed off and theolodolite levelling was also closed back to eliminate errors. I would say that the results they achieved were just as good as modern satellite images, its just that they took longer to do it, used more equipment and things could be missed. But what they did find and measure was done accurately and precisely. 

OS claim modern satellite based maps are more accurate than earlier efforts, so that's what I was using to make my comment.

[Nick C]

32 minutes ago, melmerby said:

OS claim modern satellite based maps are more accurate than earlier efforts, so that's what I was using to make my comment.

They probably are - though it's precision that matters here, not accuracy...

 

A bit like as saying it's 3pm vs it's 14:54:37.535 - the first is accurate but not very precise, the other is precise, but not accurate!

[ikcdab]

1 hour ago, melmerby said:

OS claim modern satellite based maps are more accurate than earlier efforts, so that's what I was using to make my comment.

Yes and then pragmatism comes into play. Our Victorian surveyors could plot objects to within an inch or two whereas the modern OS is doing it down to sub millimeter accuracy.  The former is perfectly adequate for all normal purposes.

[Reorte]

On 30/11/2022 at 15:42, ikcdab said:

Yes and then pragmatism comes into play. Our Victorian surveyors could plot objects to within an inch or two whereas the modern OS is doing it down to sub millimeter accuracy.  The former is perfectly adequate for all normal purposes.

 

There's also the question of just what you're measuring. The location and dimensions of a building on an old OS map I'd be quite happy to assume as accurate to any degree that I'm ever likely to need, but the general topography of the land will be noticeably better surveyed on a modern map. Only a limited number of contours were surveyed once upon a time, and often that would be from a distance, with ones in between interpolated between the surveyed ones (I've seen older maps which states which contours were surveyed).

[ikcdab]

6 hours ago, Reorte said:

 

There's also the question of just what you're measuring. The location and dimensions of a building on an old OS map I'd be quite happy to assume as accurate to any degree that I'm ever likely to need, but the general topography of the land will be noticeably better surveyed on a modern map. Only a limited number of contours were surveyed once upon a time, and often that would be from a distance, with ones in between interpolated between the surveyed ones (I've seen older maps which states which contours were surveyed).

Yes correct.  Strictly, all contours must be surveyed. The ones that are interpolated are called "form lines".

I spent many years surveying contours from aerial photographs.  Using a stereoscopic device, I chased a dot along the ground to draw in contours.  Actually it was very enjoyable, and my contours still exist on published maps.