Decimal Places   Aprox. Distance    Say What?
1                10 kilometers      6.2 miles
2                1 kilometer        0.62 miles
3                100 meters         About 328 feet
4                10 meters          About 33 feet
5                1 meter            About 3 feet
6                10 centimeters     About 4 inches
7                1.0 centimeter     About ½ an inch
8                1.0 millimeter     The width of paperclip wire.
9                0.1 millimeter     The width of a strand of hair.
10               10 microns         A speck of pollen.
11               1.0 micron         A piece of cigarette smoke.
12               0.1 micron         You're doing virus-level mapping at this point.
13               10 nanometers      Does it matter how big this is?
14               1.0 nanometer      Your fingernail grows about this far in one second.
15               0.1 nanometer      An atom. An atom! What are you mapping?

Decimal Places   Aprox. Distance    Say What?
1                10 kilometers      6.2 miles
2                1 kilometer        0.62 miles
3                100 meters         About 328 feet
4                10 meters          About 33 feet
5                1 meter            About 3 feet
6                10 centimeters     About 4 inches
7                1.0 centimeter     About 1/2 an inch
8                1.0 millimeter     The width of paperclip wire.
9                0.1 millimeter     The width of a strand of hair.
10               10 microns         A speck of pollen.
11               1.0 micron         A piece of cigarette smoke.
12               0.1 micron         You're doing virus-level mapping at this point.
13               10 nanometers      Does it matter how big this is?
14               1.0 nanometer      Your fingernail grows about this far in one second.
15               0.1 nanometer      An atom. An atom! What are you mapping?

Here's my rule of thumb table...

Latitude coordinate precision by the actual cartographic scale they purport:

Decimal Places Aprox. Distance Say What? 1 10 kilometers 6.2 miles 2 1 kilometer 0.62 miles 3 100 meters About 328 feet 4 10 meters About 33 feet 5 1 meter About 3 feet 6 10 centimeters About 4 inches 7 1.0 centimeter About ½ an inch 8 1.0 millimeter The width of paperclip wire. 9 0.1 millimeter The width of a strand of hair. 10 10 microns A speck of pollen. 11 1.0 micron A piece of cigarette smoke. 12 0.1 micron You're doing virus-level mapping at this point. 13 10 nanometers Does it matter how big this is? 14 1.0 nanometer Your fingernail grows about this far in one second. 15 0.1 nanometer An atom. An atom! What are you mapping?

Here's my rule of thumb table...

Latitude coordinate precision by the actual cartographic scale they purport:

Decimal Places   Aprox. Distance    Say What?
1                10 kilometers      6.2 miles
2                1 kilometer        0.62 miles
3                100 meters         About 328 feet
4                10 meters          About 33 feet
5                1 meter            About 3 feet
6                10 centimeters     About 4 inches
7                1.0 centimeter     About ½ an inch
8                1.0 millimeter     The width of paperclip wire.
9                0.1 millimeter     The width of a strand of hair.
10               10 microns         A speck of pollen.
11               1.0 micron         A piece of cigarette smoke.
12               0.1 micron         You're doing virus-level mapping at this point.
13               10 nanometers      Does it matter how big this is?
14               1.0 nanometer      Your fingernail grows about this far in one second.
15               0.1 nanometer      An atom. An atom! What are you mapping?