Use the window below to search published control mark data made freely available from the National Geodetic Survey (NGS) web-site (

Navigation Guide

Map Tab: Use the Map tab to navigate to a location bounded by a viewing window no greater than 2 degree of latitude by 2 degree of longitude. The limits of the current view are shown at the lower right of the Map tab (see below). To navigate to the area of interest:

  • “zoom” using the slider control on the left side of the Map tab, or,
  • “zoom” using the mouse wheel, or,
  • “zoom window” by holding the Shift key and while left-clicking two points to define a rectangular area, or,
  • “pan” by left-clicking and dragging the image to the desired position in the Map tab.

Type: Select the type of the NGS markers that are to be returned.

Order: Select the positional order of accuracy of the NGS markers that are to be returned.

Stability: Select the elevational stability of the NGS markers that are to be returned..

Symbol Size: Use the horizontal slider to adjust the symbol size of the NGS markers.

Search for Control: Click on this button to initiate the search for NGS control markers that satisfy the search criteria.

Additional Notes:

  • The Search Survey Control dialog box is re-sizeable and contains re-sizeable controls.
  • Order – For additional information on Order accuracy, reference
    Horizontal A-order stations have a relative accuracy of 5 mm +/- 1:10,000,000 relative to other A-order stations. Horizontal B-order stations have a relative accuracy of 8 mm +/- 1:1,000,000 relative to other A-order and B-order stations.
    Additional information can also be viewed at
  • Stability – For additional information on marker Stability, reference
    Stability code A = expected to hold an elevation. Examples: rock outcrops; rock ledges; bedrock; massive structures with deep foundations; large structures with foundations on bedrock; or sleeved deep settings (10 feet or more) with galvanized steel pipe, galvanized steel, stainless steel, or aluminum rods.
    Stability code B = probably hold an elevation. Examples: unsleeved deep settings; massive retaining walls; abutments and piers of large bridges or tunnels; unspecified rods or pipe in a sleeve less than 10 feet; or sleeved copper-clad steel rods.
    Stability code C = may hold an elevation but subject to ground movement. Examples: Metal rods with base plates less than 10 feet deep; concrete posts (3 feet or more deep); large boulders; retaining walls for culverts or small bridges; footings or foundation walls of small to medium-size structures; or foundations such as landings, platforms, or steps.
  • As NGS markers are retrieved, left-click on the marker itself to see summary information about the marker.
  • To retrieve the NGS datasheet with additional information about the marker, left-click on the Identifier hyperlink. To close a “balloon” marker on the Map tab or an NGS datasheet, left-click on the “X” icon of the balloon or datasheet tab, respectively.
  • If any NGS datasheet tabs are open and the OK button is clicked on the dialog box, you will be prompted if the open NGS markers should be saved to the current coordinate file.