Maidenhead grid squares are the world location system every ham uses. A 6-character grid like FM18lw (Annapolis, MD) pins your QTH to within a few kilometers, short enough for daily-use logging, long enough not to give away your exact street address. All math runs in your browser. Nothing is stored.
Each level adds one resolution step (field, square, subsquare, extended). The visual above highlights where your current grid sits at each level. Full reference on how the encoding works →