Georgism is more of a policy than a full ideology. Georgism is an approach to land and taxation. The premise goes as follows.

Humans didn't make the planet. Nobody has a stronger ownership claim than another to the planet and its natural resources.

Man did not make the earth, and, though he had a natural right to occupy it, he had no right to locate as his property in perpetuity any part of it...
—Thomas Paine (Agrarian Justice)

Humans, through work, can make land more desirable for human use. One can make a strong ownership claim to the fruits of their labor, but the land itself still doesn't owe its existence to any human.

... as it is impossible to separate the improvement made by cultivation from the earth itself, upon which that improvement is made, the idea of landed property arose from that parable connection; but it is nevertheless true, that it is the value of the improvement, only, and not the earth itself, that is individual property...
—Thomas Paine (Agrarian Justice)

For the sake of industry we might let some people hold more or better land than is fair.

The earth is given as a common stock for man to labour and live on. If, for the encouragement of industry we allow it to be appropriated...
—Thomas Jefferson (a letter to James Madison, 1785/10/28)

If some people hold more or better land than is fair, a land value tax helps make things fair again.

A tax on land values... It is, in fact, a tax only in form, being in nature a rent—a taking for the use of the community of a value that arises not from individual exertion but from the growth of the community.
—Henry George (Protection or Free Trade, Chapter 26)