What is mean by electromagnetic spectrum? of what type of waves does it consist?

Set of electromagnetic radiation.

Explanation:

The electromagnetic spectrum is the energetic distribution of the set of electromagnetic radiation. It consists of electromagnetic waves, which are composed by an electric field and a magnetic field. Every object emits and absorbs these kinds of radiations. This spectrum encompasses from Gamma rays, which are highly energetic electromagnetic waves with high frequency and short wavelength, to Radio waves, which are low energetic electromagnetic waves with low frequency and long wavelength. The visible light, like the sunlight, is only a tiny portion of the electromagnetic spectrum, the rest of the electromagnetic waves are invisible to the human eye, like infrared light, UV light, X-rays, and microwaves, but they can be perceived and be measured with proper filters.

answer; they use longitude and latitude and   global grid system; good luck