The saltire is an alternative name of the Scottish flag. The white cross diagonally spanning a blue background, represents Saint Andrew, and is considered the oldest flag in Europe and the Commonwealth. .
Saint Andrew was one of the original apostles. The X-shaped cross became his symbol after had been crucified by the Romans at Patras, Greece in A.D. 60. It is believed that Saint Andrew thought himself unworthy to be crucified on a cross like that of Christ. So, at his own request, he met his end on an X-shaped cross, called a crux decussatawas, and commonly known as a saltire.
There is a legend linking the adoption of Saint Andrew's cross as Scotland’s national flag. In 832, on the eve of a battle between a combined Picts and Scots army and an invading army of Angles led by King Aethelstan of East Anglia, Saint Andrew appeared to the king of Picts, Óengus mac Fergusa, and assured him of victory. It is believed that the following morning a cloud formation gathered against the backdrop of a clear blue sky, depicting a white saltire that was visible to both sides. The king vowed that if he gained the victory, then Andrew would be the patron saint of Scotland. The Scots won. So Saint Andrew was adopted as a patron saint, and the saltire became the flag of Scotland.
The Scottish saltire is also used outside Scotland. After the Spanish colonies became independent, the inhabitants of the islands of San Andrés, Providence and Saint Catherine in the Caribbean sea voluntarily adhered to the Republic of Gran Colombia in 1822. The largest island of the archipelago is called San Andrés and its capital is San Andrés. Unsurprisingly, the flag of Colombia, San Andrés and Providencia, uses a white Saint Andrew's cross and... on a blue field like on the Scottish flag.
The saltire is also the flag for Tenerife which is the most similar to the Scottish one. The flag was initially adopted in 1845 by Royal Order. The saltire is the flag of Tenerife by an Order issued on 9 May 1989.
The flag of this Canary island indeed closely resembles the flag of Scotland, the difference is a navy blue field - a darker shade of blue than the Scottish. If navy blue is identified with the sea, the white is associated by the local people with the snow-covered peaks of the Teide volcano.
On the island of Tenerife, there are two popular versions explaining the close resemblance. It is said that the most influential masters of the island of Tenerife chose a design similar to the Scottish flag belonging to Scottish Rite, the Masonic Grand Lodge of Scotland, and proposed a similar flag for the maritime province of the Canary Islands, which later became the flag of Tenerife. However, according to the most common theory, the flag was adopted just as a mark of respect to the bravery of the Scottish sailors in the Battle of Santa Cruz of 1797, an amphibious assault by the Royal Navy on the port city of Tenerife.
Some cities, towns and villages also use a white saltire on a blue field. In Poland, the second-largest city, Kraków, was twinned with Edinburgh in 1995. By coincidence, the official banner of the city feature the coat of arms of Kraków overlying a white saltire on a blue field.
In Spain you can find a Scottish flag 'twin' in Basque Country and Catalonia. Arrigorriaga is a town and municipality located in Biscay province, a part of Bilbao's metropolitan area. The flag of Arrigorriaga has the saltire framed with a red border.
Catalonia has two small villages which have flags closely resembling the Scotland's flag, though with peculiar details. The flag of a small village named Ivars d'Urgell, located in Lleida province has a white cross on a quite blue field with a red eight-pointed star on its centre.
The flag of the village of Ullà in Gerona province consists of a white saltire in a light blue field with the fleur-de-lis (the lily) superimposed in the centre. By coincidence, a red double border with fleurs-de-lis decorates the royal arms of Scotland that feature a red rampant lion with blue tongue and claws. Incidentally, a rampant lion is depicted on the coat of arms of Torrox.