Question re Griffith's Maps

[TreeTreeTree]

We are researching our family history and we have found our ancestral home on Griffith's maps.

The number "1750" is marked within out plot and the map dates back to Anglo-norman times, so we know it isn't a date.

The plot is "Coolfin Castle" - 1/2 km south of Abbey Village in South East Galway.

Anyone know what the number represents?

Screenshot of the Plot attached here in PDF

and here is the website link:https://griffiths.askaboutireland.ie/gv4/single_layer/i8.php?lat=&longt=&dum=0&sheet=125,126&mysession=2914958614472&info=&place=&county=Galway&placename=%3Cb%3ECoolfin%3C/b%3E&parish=Ballynakill&country=Ireland&union=&barony=Leitrim

[MollyC]

The map appears to be overprinted on an Ordnance Survey base map at 1:2500 ("twenty-five inch") scale, which will be 19th cent. or later.  The number seems to be a spot height in feet, a dot marking an accurately surveyed point, given that there are no contours on this series.  Spot heights are often on summits or along roads.  Compare it with a contoured map of the district to see if that makes sense.

Added: I think the number is 175, plus a tree or a circular enclosure - which is not very clear.

[AlanBoyd]

Here's a link to the map at NLS.
https://tinyurl.com/davzhn4y

It's clear, as MollyC says, that the number is 175, and the hypothetical zero is actually a symbol. If you zoom out a little you'll see several of these scattered about. According to this key, the symbol represents a lime kiln:

https://maps.nls.uk/os/characteristic-sheets/index.html


added: streetview
https://maps.app.goo.gl/hCmhbqBgjQYHduk17?g_st=ic

[Kiltaglassan]

..and here's Coolfin Castle (in ruins) off the R353. On a slight rise so maybe it's height above sea level of 175 ft.

https://www.rootschat.com/links/01t3r/


Added:
Snap! AlanBoyd

[MollyC]

I was incorrect, it is a six-inch map, difficult to tell when zooming on the screen.  The Irish series has a different specification to the Great Britain series which I am used to, those have 25ft. contours.  The Irish ones are earlier, c1830-40, arising out of a decision to send most of the OS surveyors there to sort out land-rent problems by mapping the townlands.  The one-inch scale was not large enough so the six-inch was developed for Ireland, then continues initially in northern England and central Scotland, before the 1:2500 was commenced c1858.  These early engraved maps have a special soft quality which was lost when production moved over to lithography.

[TreeTreeTree]

This is an amazing forum! Thank you so much for sharing your knowledge all!