Art is...

a form of communication. Mostly it is the art of the artist to criticize environment, social or political influences or through aesthetics leading to a world of beauty, imagination and sensual pleasures. Originally the shamans were the artists which in a ritual with visuals, music, dance or with a staging opened the portal to another world to induce initiation or healing.
Sandpictures cover all three aspects. Comments

The Brockhaus encyclopedia wrote in 1955 about art:

1. Basically: each skill brought to mastery, turning ability into proficiency.
2. Fine arts: art is the arrangement of a spiritual-mental content with a particular art form following particular rules. The means of composing and rules of their application are different for every art form. The aesthetic has proven particular form elements like proportion, rhythm, harmony and beauty.

60 years later Wikipedia knows about art:

(...) art is a human cultural product, the result of a creative process.
The artwork stands at the end of the process, since the modernity it can be the act by itself. Practitioner of art are basically called artists. (...)
Form of expression and techniques of art have developed a lot since the start of modernity, (...)
The former classification has lost importance since the last decades of the 20th century. Art forms like installation or the field of media art are not known in the classic allocation.

And what is your opinion?

On our flip chart you could read the following key words after asking the sand crew:
What are Sandpictures provoking with humans?

relaxation
happiness
like
recalls memories
change
fantasy
therapy
nature
Meditation

Sandman then summarized those comments into:
Sandpictures are a world peace mission, bringing humans calm, relax and hence peace. May all wars be ending soon and peace take place amongst humankind. Only a dream?
Being the Sandman I am allowed to dare the big dreams!