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. United States National Map Accurscy Standards (AI Horizontal accuracy-For maps on publication scales larger than 1/20,000, not more than 20 percent of the pOints lested shall be In error by more than 1/30 inch, measured on the publication scale; for maps on publication scales of 1 :20.000 or smaller. 1/50 inch. These limits of accuracy shall apply in all cases to positions of well.defined POints only. Well-defined points are those that are easily visible or recoverable on the ground. such as the following: monuments or markers. such as bench marks. property boundary monuments: intersections of roads. railroads. etc.; corners of large bUildings or structures (or center points of small buildingS); etc. In general what is well.defined wlli also be determined by what IS plottable on lhe scale of the map within 1/100 inch. Thus while the inter section at two road or property lines meeting at right angles would come wIthin a sensible Interpretation. identification of the intersection of such lines meeting at an acute angle would obviously not be practicable with 1/100 inch. Similarly. features not identifiable upon the ground within close limits are not to be considered as best points within the limits Quoted. even though their posltlons may be scaled closely upon the map. In this class would come timber lines. soil boundaries, etc. IBI Vertical accuracyuAs applied to contour maps on all publication scales, vertical accuracy Shalt be such that not more than 10 percent of the elevations tested shall be In error more than one-half the contour Interval In checking elevations taken from the map. the apparent vertical error may be decreased by assuming a horizontal displacement within the permISSIble hOrizontal error for a map of that scale lel The accuracy of any map may be tested by comparing the positions of pOints whose locations or elevatIons are shown upon It with corresponding positions as determined by surveys of a higher accuracy. Tests shall be made by the producing agency. which shall also determine wt'1lch of .ts maps are to be tested. and the extent of such testing. 10] Published maps meeting these accuracy requIrements shaH note thiS fact on their legends. as follows: "ThiS map compiles with national map accuracy standards," IE] Published maps whose errors exceed those aforestated shall omit from theIr legends all mention of standard accuracy. IF] When a published map IS a conSiderable enlargement of a map draWing imanuscript) or of a published map, that fact shalt be stated In the legend. For example "ThIS map is an enlargement of a 1 :20.000-scale map draWing:' or "ThiS map IS an enlargement of a 1 :24,OOO'scale published map."' [G] To factlitate ready Interchange and use of baSIC Information for map con- struction among all federal mapmaking agenCies. manusCript maps and published maps, wherever economically reasonable and conSistent with the uses to whIch the map IS to be put. shalt conform to latitude and longitude boundanes. berng 15 minutes of latitude and longitude, or 7 5 minutes, or 3- 3/4 minutes 10 size. . local governmenls can use the National Map Accuracy Standards as thelf basic crrteria In determIning whether maps for whIch they will enter Into a contract or eXisting maps they use are sufficiently accurate. If maps meet the National Map Accuracy Standards. that fact must be stated on the maps. .