Colby, Thomas Frederick (1784–1852), engineer and administrator, was born 1 September 1784 at Rochester, Kent, England, eldest child of Maj. Thomas Colby (Royal Marines) of south Wales, and Cornelia Colby (née Hadden), both of military families. Educated at Northfleet, Kent, and the Royal Military Academy, Woolwich, he was commissioned in the Royal Engineers at 17; three weeks later he was assigned to the ordnance survey, in which he spent the rest of his career. Despite mutilation in a gun accident (1803) Colby distinguished himself in field surveying, calculation, technical development, and administration. From 1809 he was chief executive officer of the survey, and in 1820 the duke of Wellington (qv), on scientific advice, made him superintendent in preference to senior officers.
In 1824, on the initiative of Irish MPs, a comprehensive survey of Ireland was instituted on a townland basis to rationalise land valuation and local taxation, boundaries being determined by a valuation department under Richard Griffith (qv). With a view to uniformity and control, mapping these boundaries was entrusted – largely on Colby's advice – to the ordnance department instead of private surveyors. This involved creating a substantial body of technical experts under military discipline (and Colby's own procedural code), from which Ireland gained the under-secretaries Thomas Drummond (qv) (1835–40) and T. A. Larcom (qv) (1853–68). Colby's period in Ireland (1824–38) determined the character of official mapping there. Beside developing improved measuring equipment and methods, he developed his department's role beyond the immediate needs of valuation into an unprecedented programme: to produce a unified six-inch map of all Ireland, printed and published for public sale, and amplified (in ‘memoirs’ recording topographic, historic, and even linguistic data) into a comprehensive tool of social and economic reference.
Reconciling accuracy, comprehensiveness, and progress was not easy. Colby, who combined meticulousness with distaste for ‘ornamental’ knowledge, clashed variously with the treasury, Griffith, Drummond, Larcom, and others on the balance of priorities, and the breadth of treatment in the first local ‘memoir’ (published 1833) could not be sustained. However, the six-inch map (published 1833–46) was a milestone in map drawing and production; the ancillary research stimulated much scholarly activity, including the establishment of a geological survey. Colby returned to London in 1838, moving (with ordnance survey headquarters) to Southampton in 1842, but continued active involvement with the Irish survey till his retirement as a major-general in 1846. His career showed him capable of bitter disagreement with others, but also of great generosity, complete professional dedication, and unconcern for personal advancement, and he devoted much of his salary to his department. He was a member of the RIA and many other scientific and professional bodies, a knight of Denmark, and an honorary LLD (Aberdeen). He married (1828) Elizabeth Hester, second daughter of Archibald Boyd, treasurer of Co. Londonderry; they had four sons and three daughters. They lived in Mountjoy Square, Dublin (1828–30) and in Knockmaroon Lodge, near survey headquarters in Phoenix Park (1830–38); after Colby's retirement, the family went to the Continent (1847–8) for the sake of his sons' education. He died (2 October 1852) at New Brighton, Cheshire. His widow's life pension was the only state acknowledgement of his service.