When searching ScotlandsPeople it sometimes seems to list two parishes together. For example:
- Urquhart and Glenmoriston
- Old or West Kilpatrick
- Ardnamurchan and Strontian or Sunart
Why would this be?
There are several different reasons.
For the first example, Urquhart and Glenmoriston, that is the name of the parish, it consists of two places that were previously separate parishes but later combined into one.
Old or West Kilpatrick are two alternate names for the same parish. Apparently the West or Wester name was only used for a while in the 1600's, after a split with the east (new) side of Kilpatrick.
Strontian or Sunart are again two alternative names for the same place (the village of Strontian is in the Sunart area). These were previously part of Ardnamurchan and in an area of very low population so Scotlands People still combines them.
I fear that you have misinterpreted your source.
A Vision of Britain provides detailed authoritative information on political and administrative jurisdictions for Britian, including Scottish Parishes. For example, the entry for Urquhart and Glenmoriston informs us that the parish was created in 1845 and abolished in 1975 and includes a boundary map and summary statisics derived from censuses.
In addition to A Vision of Britain which was already recommended, here are some other resources for finding information about places in Scotland:
For a demo of many of these websites, there is a series of webinars on Scotland Research, produced by the FamilySearch British Isles team. See the section on previous webinars for the class Scotland Maps and Gazetteers (the handout by Dan Poffenberger, AG is available for download). The classes on Scotland Church Records may also be of interest.