Research and understand mattes and matte painting

1) A matte painting is a painted representation of a set, landscape or distant location which allows filmmakers to create the inclusion of an environment that is non-existent in real life or would otherwise be too expensive or impossible to build or visit. Artists would set up a large plate of clear glass in front of the motion picture camera upon which he would carefully paint in a new scenery for example snow capped mountains.

2) History of Matte Painting:
Matte paintings were made by artists using paints or pastels on large sheets of glass for integrating with the live action footage. In 1907, the first known matte painting shot was made by Norman Dawn, who improvised the crumbling California Missions by painting them on glass for the movie 'Missons of California'. Other traditional matte paintings shots include Dorothy's approach to the Emerald city in The Wizard of Oz as well as the seemingly  endless tractor-beam set of Star Wards Episode IV: A New Hope. The first documentary of Star Wars (The Making of Star Wars) mentioned the technique used for the tractor beam scene as being a glass painting. By the mid 1980's, advancements in computer graphics programs allowed matte painters to work in the digital realm as the first digital matte shot was created by painter Chris Evans in 1985 for 'Young Sherlock Holmes' for the scene featuring computer graphics animation of a knight leaping from a stained-glass window.  His first painted the window in acrylics, then scanned the painting into LucasFilm's Pixar system for more digital manipulation. This blended perfectly with the digital matte.
In 1902, filmmaker Georges Melies made 'Le Voyage dans la Lune' and to create special effects he had to paint some curtains to use as a back drop and had to use an actual man in a moon costume for a man on the moon.

3) Wizard of Oz used matte painting for when they are approaching the Emerald City. It was used because there is nothing in real life resembling Emerald City so there only option was to draw it as a matte painting. I don't find this matte very convincing and quite poor, because the characters are quite faint compared to the image. I find the background looks quite cartoon like, when there is real people there.