What is the difference between analog and digital communications?

What are the main differences between using analog or digital communications? Why is digital communications considered a better form of communications?

An analog signal represents a value by varying voltage levels. When transmitting the varying voltage representation, it is subject to outside noise and EMI/RFI.

Due to the noise and distortion possibilities of an analog signal, the value, resolution and accuracy is limited. The analog signaling system using 4-20 ma has a resolution of 16,000, or 14 bits. The typical digital signal has a resolution of 1,048,576, or 20 bits.

A digital signal represents a value that is captured at the source and then transmitted in a format of ones and zeros that are subject to error checks for validity. With this error checking you are assured the value measured was properly reproduced.

Digital communications is more accurate than analog communications.