One of the big pieces of work that the Ordnance Survey staff did in Ireland was compile the raw data for Griffiths Valuation (1848 – 1864). They travelled the country starting at the south, and working up to the north, valuing almost every property and every piece of land in the country. The results of that survey can be found on the Griffiths Valuation site:
http://www.askaboutireland.ie/griffith-valuation/index.xmlThough this detailed study wasn’t started till 1848 there was an earlier assessment made in the 1830s, in field notebooks (many of which have survived). So there were OS staff travelling the length of the country in the 1830s gathering valuation data (to be used for land taxation purposes). That could explain James’ presence in any or indeed every county in Ireland, if he was working for them at that time.
The OS survey was organized by the army often using Royal Engineers staff, but there were also civilian assistants. So James might have been in the army, or he might have been employed in a civilian capacity.
Regarding the lack of children between 1837 & 1843, there may have been children that died and there might not be a record of them since birth & death registration didn’t start in Ireland till 1864. The Church of Ireland does generally keep baptism and burial records (though not every burial was recorded). However only a small proportion of those records are on-line. For many you need to search the original parish records, which in some cases are in the Representative Church Body (RCB) library in Dublin and in others held by the local Minister. A personal visit is generally required to search them. But if you don’t know where in Ireland he was living, there’s no easy way to identify the correct records. They haven’t all survived anyway. Many early Church of Ireland records were lost in the 1922 fire in Dublin.
My Church of Ireland guide says that the records for Oughaval (also spelled Aughaval) are in the RCB library. Baptisms & marriages start in 1801 and burials in 1820. It also says that some of those records are on the rootsireland site. So evidently they don’t have them all. And obviously if James subsequently moved to another parish (as would be likely if he was working for the OS) then their records may not have survived, or may not be on-line.