What data is necessary to make an accurate contour map? how is this information gathered?

Thank you for posting your question here. depends on what kind of contour map you want - you generally need point locations (x,y or lat,longs) and then some kind of data value at each point. Elevation is one of the most common types of data used for contouring (eg. topographic maps), but many other kinds of information are also contoured: magnetic or gravity field readings, water or air quality measurements, sea surface temperatures, weather data, the list goes on and on... You can create countours by hand or use a software package to create them for you... and of course, the more points you have, the more accurate your contour map will be!