| RHP1220 | Plan of the estate of Castlehill, Olrig, Caithness | 1772 |
| RHP1221 | Plan of the Mains of Castlehill | nd |
| RHP8720 | Plan of Thurso Bay from the point of Holborn Head to Clardon Head and the coast to Castlehill (Vignettes of sailing vessels) (1-2) | 1789 |
| RHP11612 | Plan of intended road from Huna (Houna) Inn to the town of Thurso. | 1798 |
| RHP13135 | Sketch plan of Castlehill Harbour | 1891 |
| RHP22512 | Plan of proposed line of [Highland Railway] passing through Cleanie (Clenny) Moss | c 1871 |
| RHP22515 | Architectural sketch plan of house and barn for Ha' of Durran | 1860 |
| RHP22516 | Architectural plan and elevation of William Durran's proposed dwelling house at [?Durran] | Late 19th century |
| RHP43652 | Ordnance Survey 1/2500 plan marked to show Castletown Drainage and Water Supply Districts. | 1931 |
| RHP43655 | Plan of lands of Murkle, with numbered divisions. | [20th century] |
| RHP43671 | Ordnance Survey 6 inch plan marked to show proposed new and enlarged holdings and acreage of arable land and pasture on these, on farms of Broynach and Mayfield. | 1913 |
| RHP78982 | Ordnance Survey 6 inch plan (Caithness, sheet XI) marked to show farm boundaries | [1944-1955] |
| RHP78983 | Ordnance Survey 6 inch plan (Caithness, sheet XII) marked to show farm boundaries | [1944-1955] |
| RHP79524 | Ordnance Survey 6 inch plan (Caithness, sheet V) marked to show farm boundaries: [1944 x 1954] | nd |
| RHP79525 | Ordnance Survey 6 inch plan (Caithness, sheet VI) marked to show farm boundaries: [1944 x 1954] | nd |
| RHP97560 | Ordnance Survey 6 inch plan (Caithness, sheet V) coloured to show classification of land | [1944-1954] |
| RHP142769 | Ordnance Survey [-] plan (Caithness) | c 1910 |