Synthetic plastics are made by linking many simple carbon molecules together to form much larger molecules. the process is called

Polymerization

Explanation:

Several natural and man-made organic compounds are enormous molecules which contains hundreds of thousands of atoms per molecule.

The giant molecules formed are produced through the process of polymerization.

Polymerization is the linking of monomers through chemical reactions to form long chain polymer molecules.

Monomers are small molecules that are joined to form polymers.

Synthetic plastics are derieved from synthetic polymers. These synthetic materials are very useful and vital due to their great size. Their size premits a certain complexity of structure which makes the molecules disposed in a regular pattern with respect to one another. They stretch out nearly to alongside of one another or coil up independently. The polymerization of monomers to form plastics fosters the various uses these giant molecules are put to.

in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation:

it is the most commonly accepted one