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Home My WebLink AboutWPO201500015 Plan - Other (not approved) WPO VSMP 2015-07-01 Y i fla N isP 11 ii I Lt } I 1 ' .0 litetpit l3 i bIi plisil 1 liai IMilli oisPiiiilii '''').).::4 # .';1.-== ell o c2 IP' L rn c o �° oa 111: ii) -1 P f del 40* T 44. 10' . i 4,ikrikk -- --,/ United States National Map Accuracy Standards With a view to the utmost economy and expedition in producing maps which fulfill not only the broad needs for standard or principal maps,but also the reasonable particular needs of individual agencies, standards of accuracy for published maps are defined as follows: 1. Horizontal accuracy. For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested 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 will be determined by what is plottable on the scale of the map within 1/100 inch. Thus while the intersection of 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 within 1/100 inch. Similarly,features not identifiable upon the ground within close limits are not to be considered as test points within the limits quoted,even though their positions may be scaled closely upon the map. In this class would come timber lines,soil boundaries,etc. 2. Vertical accuracy, as applied to contour maps on all publication scales, shall 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. 3. 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 which of its maps are to be tested, and the extent of the testing. 4. Published maps meeting these accuracy requirements shall note this fact on their legends,as follows: "This map complies with National Map accuracy Standards." 5. Published maps whose errors exceed those aforestated shall omit from their legends all mention of standard accuracy. 6. When a published map is a considerable enlargement of a map drawing(manuscript)or of a published map,that fact shall 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 1:24,000-scale published map." 7. To facilitate ready interchange and use of basic information for map construction among all Federal mapmaking agencies,manuscript maps and published maps,wherever economically feasible and consistent with the uses to which the map is to be put, shall conform to latitude and longitude boundaries,being 15 minutes of latitude and longitude,or 7.5 minutes,or 3-3/4 minutes in size. Issued June 10, 1941 U.S.BUREAU OF THE BUDGET Revised April26, 1943 Revised June 17, 1947 Justin Deel From: Elise Hackett Sent: Thursday, October 08, 2015 3:19 PM To: Justin Deel; Andrew Slack Cc: Damon Pettitt Subject: FW: County topological data accuracy Justin, Damon helped me out and below seems to be the accuracy of the data. It seems 2'—2.4'. If your customer has something that is more accurate than that then I guess you guys would need to decide if you accept it or not.As far as protocol in the future if you want to update the Steep Slopes layer itself I would guess that would be up to Bill. nterval: 4 feet Orthophotography: 1 foot resolution "Standard" Scal (1:2400) Mass Point / Breakline Vertical Accuracyz (NSSDA @ 95%): 2' to 2.4' Overall DTM an on o Vertical Accuracyz (NSSDA @ 95%): 2' to 2.4' Elise Hackett, GISP GIS Specialist II Division of Information Services http://gisweb.albemarle.org 434-296-5832 ext. 3030 From: Damon Pettitt Sent:Thursday, October 08, 2015 2:33 PM To: Elise Hackett<ehackett@albemarle.org> Subject: FW: County topological data accuracy Damon Pettitt,GISP Senior Systems Analyst for Fire Rescue I Albemarle County,VA (434)296-5833 ext.3231 I dpettitt@albemarle.org I www.albemarle.org/firerescue If you must print this email or any attachments, consider using the back of already printed paper. From:Justin Deel Sent:Wednesday, October 07, 2015 3:12 PM To: Damon Pettitt<DPETTITT@albemarle.org>;Andrew Slack<aslack@albemarle.org> Subject: RE: County topological data accuracy Thank you, Damon and Andy! This is very helpful. Justin From: Damon Pettitt Sent: Wednesday, October 07, 2015 3:01 PM To:Andrew Slack<aslack@albemarle.org> Cc:Justin Deel<ideel@albemarle.org> Subject: RE: County topological data accuracy The accuracy information of our topography(most recently from 2013 orthos) should be in the metadata. 1 r (.4 4.0 Also, if someone is having questions about the steep slopes(no longer called critical slopes),then they should talk to , Bill. Elise may also know some info about the accuracy question as she helped Bill define these areas and also what the protocol is if someone things these areas are not accurate. Damon Pettitt,GISP Senior Systems Analyst for Fire Rescue I Albemarle County,VA (434)296-5833 ext. 3231 I dpettitt@albemarle.org I www.albemarle.org/firerescue If you must print this email or any attachments,consider using the back of already printed paper. From: Andrew Slack Sent: Wednesday, October 07, 2015 2:57 PM To: Damon Pettitt<DPETTITT@albemarle.org> Cc:Justin Deel <ideel@albemarle.org> Subject: County topological data accuracy Damon, Justin Deel(cc'ed)came by with a question today. How accurate are our contour lines and would it be reasonable to say that a more accurate topology could be found by newer aerials? The reason this is coming up is because and engineering firm is trying to say that some of our critical slope areas are not correct and they believe that they have some new topo from more current aerial photography that shows the slope areas being smaller. Andy Slack GIS Specialist II Information Services-Department of Community Development Albemarle County,VA Phone: (434)296-5832 ext. 3384 Email: aslack(a,albemarle.org www.albemarle.org 2