The Union Canal is a contour canal, following a 73 metre (240ft) contour throughout its length. Originally, the only locks were those at Falkirk, to make the link to the Forth and Clyde canal. Now, there is one lock just before the Falkirk Wheel and a double lock just above. There is also a new tunnel where the canal passes under the Antonine Wall.

The canal has many aqueducts, including the Slateford Aqueduct that takes the canal over the Water of Leith in Edinburgh, the Almond Aqueduct near Ratho and the 810ft long Avon Aqueduct near Linlithgow, the second longest in the United Kingdom. The Edinburgh end of the canal no longer reaches quite as far as it did (to 'Port Hopetoun' and 'Port Hamilton' basins which were filled in after the canal closed). Instead, the canal stops at Lochrin Basin at Fountainbridge. Many of the stone bridges have keystones emblazoned with the coats of arms of Glasgow and Edinburgh, facing west and east respectively.
It was originally known as the Edinburgh and Glasgow Union Canal, to celebrate the uniting of the two cities by the new canal network, but this name is rarely used today. The canal was designed by Hugh Baird, who oversaw the engineering work while it was being built between 1818 and 1822. Two of its construction workers were the famous murderers Burke and Hare. Originally used for transporting coal, competition from the railways caused it to close to commercial use in the 1930s. The locks, connecting it to the Forth and Clyde Canal at Falkirk, were filled in and built over.

The Slateford Aqueduct has eight arches, is 600 feet (180 m) long and 60 feet (18 m) tall, and carries the Union Canal across Inglis Road and the Water of Leith at Longstone (just at the edge of Slateford) in south-west Edinburgh.

The Water of Leith is the main river flowing through Edinburgh, to the port of Leith where it flows into the sea via the Firth of Forth.
It is 35 km (24 miles) long and rises in the Colzium Springs at Millstone Rig of the Pentland Hills. It travels through Harperrig Reservoir, past the ruins of Cairns Castle, through Balerno, Currie, Juniper Green, Colinton, Slateford, Longstone, Saughton, Balgreen, Roseburn and on to the nearest it gets to the city centre at the Dean Village, on the site of old watermills in a deep gorge. This ravine is dramatically spanned by the Dean Bridge, designed by Thomas Telford, which was built in 1832 for the road to Queensferry, and lies next to the New Town.

The Red Wheel Plaque was unveiled on 7th August 2023 by Richard Baird, Commander of the Clan Baird, and John Cameron CBE, Vice President of the National Transport Trust.

On the occasion John Cameron remarked: "It's splendid that both these unveilings celebrate Hugh Baird's Union Canal as a whole, and I’m delighted to be joining my fellow farmer, Clan Baird Commander Richard Holman Baird in doing the honours. This is actually the Union’s third Red Wheel, others being at the Leamington Lift Bridge and the Linlithgow Canal Basin. It's the first at one of its Aqueducts, chosen as the most visited of the three graceful iron-trough designs to be seen also at Lin's Mill and Muiravonside. As a railwayman I'm conscious of how railways ended the first Canal Age – however in their splendid repurposing, by the Millennium Link as a mode of sustainable travel, maybe it's the canals that have had the last laugh."

A historical brochure covering the history of the Baird Family engineers can be downloaded here

Photo credits: Kevin Rae / Slateford Aqueduct and Viaduct; Rosser1954,  © Copyright Mat Fascione and licensed for reuse under this Creative Commons Licence, Rosser1954, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons, John Yellowlees - with thanks