Many tactile tiles have been installed at subway stations and on sidewalks in Seoul, Korea. The installation in Seoul is more challenging than in Japan, because the surface of various sidewalks in Seoul is not flat, so there are many places where the meaning of a tactile tile is not clearly conveyed. Tactile tiles were adopted at each facility used for the Sydney Olympic Games in 2000, and are ubiquitous in Australian public transport facilities. That trend has also been apparent in the UK, the US, and throughout the world. These are used for pedestrian crossings. The purpose of the blister surface is to provide a warning to vision-impaired people who would otherwise, in the absence of a change of height of >25mm, find it difficult differentiate between where the footway ends and the carriageway begins. The surface is therefore an essential safety feature for this group of road users at pedestrian crossing points where the footway is flush to the carriageway, to enable wheelchair users to cross unimpeded. The profile of the blister tactile surface consists of rows of flat-topped blisters in a square pattern. The offset blister tactile is also known as the "platform edge (off-street) warning surface". The purpose of this surface is to warn vision-impaired people of the edge of all off-street railway platforms. The off-set blister tactile surface consists of flat-topped domes (blisters), spaced 66.5mm from the center of one dome to the next one. Tactile paving units can be manufactured in any suitable paving material and may be any color that provides a good contrast with the surrounding area, to assist partially-sighted people. The current guidance recommends that the off-set blister tactile surface be used for all off-street rail platforms including:  It should not be used for on street (LRT) platforms  The lozenge tactile is also known as the platform edge (on-street) warning surface. The purpose of the platform edge (on-street) warning surface is to warn vision-impaired people that they are approaching the edge of an on-street light rapid transit (LRT) platform. The profile of the lozenge tactile warning surface comprises rows of 6±0.5-mm high lozenge shapes, which have rounded edges so as not to cause a trip hazard. The tactile paving units can be manufactured in any suitable paving material. The surface is usually buff colored, but can be any color, other than red, that provides a good contrast with the surrounding area, to assist partially-sighted people.