Question: W.H. Walker and Brothers was a narrowboat builder based in a small town approximately 20 mi northwest of what?

full_context: Document 1: Thompson Brothers Boat Manufacturing Company: The Thompson Brothers Boat Manufacturing Company of Peshtigo, Wisconsin was a manufacturer of pleasure boats and canoes. Founded by brothers Peter and Christ Thompson in 1904, the company became prominent in the field and built boats for nearly one hundred years. The Thompson Antique & Classic Boat Rally celebrates the company's history with a boat show every other year and in 2013 the Thompson Brothers canoe was celebrated at the Annual Assembly of the Wooden Canoe Heritage Association.
Document 2: W.H. Walker and Brothers: W.H. Walker and Brothers was a narrowboat builder based in Rickmansworth, England.The business was established in 1905 by Harry Walker. He leased part of Frogmoor Wharf, the Grand Union Canal, from Robert Grosvenor, 2nd Baron Ebury. The firm thrived for most of the twentieth century, from 1905 to 1964. They were one of the major producers of narrow boats for the English Canal Network. The site was sold for redevelopment to Tesco in June 1989.
Document 3: Walker Ranch: The Walker Ranch is a historic ranch in Boulder County, Colorado. The ranch was built by James A. Walker, who first settled in the Boulder area in 1865. Walker and his family initially lived in a log cabin on the ranch, which was built in 1865. In 1881, Walker and his family built and moved to a new ranch house. Walker engaged in a number of business ventures on the ranch and leased parts of the ranch to other businessmen, and the enterprises which took place on the ranch represent many of the region's industries at the time. Walker mainly raised cattle and milled lumber on the property, and an English firm mined gold using a cyanide mill; payments from the latter operation allowed Walker to eliminate his debt and purchase additional land for the ranch. Of the remaining historic buildings on the ranch, eleven are from Walker's homestead and his ranching operations, fourteen were part of Walker's sawmill operations, and fourteen are related to the cyanide mill. The ranch also includes five archaeological sites; three of these are remnants of aboriginal settlement in the area and two of these are Arapahoe sites, including a site Walker may have shared with the Arapahoe when he first came to the area.
Document 4: Waltham Cross: Waltham Cross is a suburban dormitory town 12 miles NNE of central London and located within the metropolitan area of London, the Greater London Urban Area, and the Borough of Broxbourne in Hertfordshire. It is immediately north of the London Borough of Enfield and is the most southeasterly town of Hertfordshire, located immediately north of the M25 motorway. The Waltham Cross post town additionally includes the neighbouring town of Cheshunt and a small part of Enfield.
Document 5: T. B. Walker: Thomas Barlow Walker (February 1, 1840 – July 28, 1928) was a highly successful American businessperson who acquired timber in Minnesota and California and became an art collector. Walker founded the Minneapolis Public Library. He was among the ten wealthiest men in the world in 1923. He built two company towns, one of which his son sold to become part of what is today known as Sunkist. He is the founder and namesake of the Walker Art Center.
Document 6: Three Rivers District Council: Three Rivers District Council is the local authority for the Three Rivers non-metropolitan district of England, the United Kingdom. Three Rivers is located in the south-west of Hertfordshire, in the East of England region. The Council itself is based in Rickmansworth, the largest settlement in the district, but also comprises Abbots Langley, Chorleywood, Croxley Green, Maple Cross, Mill End, Sarratt and South Oxhey.
Document 7: Walker railway station: Walker railway station, known as Low Walker until 1889, served Walker, a residential suburb of Newcastle, in Tyne and Wear. It was situated on the North Eastern Railway's Riverside Branch from to Tynemouth via . The station served as a passenger halt and goods depot for shipping companies such as Armstrong Whitworth and other land-based companies including the Northern Wood Haskinizing Company.
Document 8: Freeman Cruisers: Freeman Cruisers was a British manufacturer of cabin cruisers that was active between the years of 1957 and 1983. It took its name from its founder, John Freeman. Freeman had been previously manufacturing caravans and towing trailers before Second World War broke out, but production ceased due to the war. In 1983, the assets of the company were sold to "Sheridan Marine", which still produces spare parts and sells used boats from their boatyard in Moulsford, Oxfordshire. Over 28 models of boat were produced by the company, and they are frequently seen on the navigable waterways of the UK. In addition, Freeman Cruisers are easily able to go to sea, with a few slight modifications to their plumbing and flushing systems.
Document 9: Rickmansworth: Rickmansworth is a small town in south-west Hertfordshire, England, situated approximately 20 mi northwest of central London and inside the perimeter of the M25 motorway. The town is mainly to the north of the Grand Union Canal (formerly the Grand Junction Canal) and the River Colne. The nearest large town is Watford, approximately 5 mi to the east. Rickmansworth is the administrative seat of the Three Rivers District Council; the local authority is named from the confluence of three rivers within Rickmansworth's borders; the River Gade and the Grand Union Canal join the upper River Colne near Rickmansworth's eastern boundary and are joined by the River Chess near the town centre from where the enlarged Colne flows south to form a major tributary of the River Thames. The town is served by the Metropolitan line of the London Underground and Chiltern Railways from London Marylebone to Aylesbury.
Document 10: River Lea: The River Lea in England originates in Marsh Farm, Leagrave, Luton in the Chiltern Hills and flows generally southeast, east, and then south through east London where it meets the River Thames, the last section being known as Bow Creek. It is one of the largest rivers in London and the easternmost major tributary of the Thames. Its valley creates a long chain of marshy ground along its lower length, much of which has been used for gravel and mineral extraction, reservoirs and industry. Much of the river has been canalised to provide a navigable route for boats into eastern Hertfordshire, known as the Lee Navigation. While the lower Lea remains somewhat polluted, its upper stretch and tributaries, classified as chalk streams, are a major source of drinking water for London. A diversion known as the New River, opened in 1613, abstracts clean water away from the lower stretch of the river for drinking. Its origins in the Chilterns contribute to the extreme hardness (high mineral content) of London tap water.
Document 11: Sarratt: Sarratt is a village and civil parish in Three Rivers District, Hertfordshire. It is situated 4 mi north of Rickmansworth on high ground near the county boundary with Buckinghamshire. The chalk stream, the River Chess, rising just north of Chesham in the Chiltern Hills, passes through Sarratt Bottom in the valley to the west of the village to join the River Colne in Rickmansworth. The conditions offered by the river are perfect for the cultivation of Cress. Sarratt has the last commercially operating cress farm in Hertfordshire. The valley to the east of Sarratt is dry.
Document 12: Chorleywood: Chorleywood is a village and civil parish in Three Rivers District, Hertfordshire. It is situated in the far south-west of Hertfordshire on the border with Buckinghamshire approximately 32 km north-west of Charing Cross. It is part of the London commuter belt and included in the government-defined Greater London Urban Area. Chorleywood as a parish was created in 1845 from part of the parish of Rickmansworth.
Document 13: Fleetsbridge: Fleetsbridge is a small area of Poole, Dorset, centred on a busy gyratory and flyover. It lies north of Poole town centre and borders the neighbouring suburbs of Waterloo, Creekmoor, Oakdale and Canford Heath. The use of land varies between residential, retail and some light industry. The area is also home to Parkstone Grammar School when it moved there from Lower Parkstone in 1962. The site of the Tesco at Fleets Corner was, up until the 1980s, the home of Hamworthy Recreation Football Club before the land was sold and the club moved to Canford Magna on the northern extreme of the Borough of Poole. Opposite to Tesco, across Waterloo Road, is the home of the headquarters of the global company, Hamworthy Combustion Engineering. Fleets Industrial Estate lies to the south of the gyratory off Fleets Lane and is adjacent to Wessex Gate Retail Park, which has large retail outlets such as DFS, Currys and PC World.
Document 14: Mill End, Rickmansworth: Mill End is a semi-rural village in Hertfordshire, England, which has in recent times become a contiguous part of Rickmansworth. Most of it is unparished (i.e. it does not have a civil parish council); part comes under Chorleywood Parish Council. By the time 0f the 2011 Census a new civil parish had been formed called Maple Cross and Mill End. All of Mill End forms part of Three Rivers District and so is administered by Three Rivers District Council and Hertfordshire County Council.
Document 15: Berkhamsted railway station: Berkhamsted railway station is in the town of Berkhamsted, Hertfordshire, England. It is located just beside Berkhamsted Castle, overlooking the Grand Junction Canal. The station is 28 mi north west of London Euston on the West Coast Main Line. London Midland operates services to London, Northampton and many other destinations.
ground_truth: central London