This is not meant to be an exhaustive list; rather, it is a place to start when you are looking for maps to help your research. Some of the entries are themselves lists of external links. Copyright is for you to assess.
See also my list of Image databases.
A vision of Britain from 1801 to now. Including maps, statistical trends and historical descriptions. Of most relevance: Ordnance Survey First Series 1:63360 (170 sheets covering England and Wales, 1805 to 1869);
C. Smith New Map of Great Britain and Ireland 1:633600 (4 sheets covering Great Britain, 1806); R. Wilkinson The British Isles 1:2000000 (1 sheet covering Great Britain, 1812). The site is run by the University of Portsmouth and partners.
Zoomable, high-resolution colour maps dating from between 1560 and 1964, primarily related to Scotland but also including England and Great Britain, Ireland, Belgium, and Jamaica. There are also maps made for military purposes and Ordnance Survey.
One of the world’s largest libraries devoted entirely to rare books and manuscripts.
Over 1 million historical map images, including Ordnance Survey County Series maps from 1843 to approximately 1996. Maps are free to view online and images can be purchased as file, prints (framed and unframed). A paid-for service (subscriptions are £9.99 per month) gives an enhanced view and discounts.
A collaborative project to index over 400,000 historical maps in archives and libraries, with many participating institutions.
Historic maps of London from before 1800 and maps from the 19th-century series of the Ordnance Survey, including the complete 1:10,560 series and selected areas of the 1:2,500 maps. The Ordnance Survey maps can searched by keyword, title or postcode. Several 17th-century maps of London.
An exhaustive Place Name Index to Great Britain, containing over 50,000 entries. It lists the historic county and the main administrative areas in which each place lies. Read the accompanying notes before using.
A list of useful map websites, with a focus on the North.
Includes a set of 52 high resolution English County maps dating from 1724.
An extraordinary labour of love, the work of one person who has generously put their non-commercial mixture of comment and tips online, along with thousands of links to free sites.
This directory lists the major map collections in the UK. It is freely available subject to the Society’s Terms and Conditions. Use the filter on the right to browse for collections, or the “Search for a Collection” box to find more specific collections.
A list of British Library map collections that are available online.