[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"blog-\u002Fblog\u002Fwhy-plss-section-boundaries-are-not-all-640-acres-blm-survey-polygons-vs-estimated-centroids":3},{"id":4,"title":5,"body":6,"cover":149,"date":150,"description":151,"draft":152,"extension":153,"meta":154,"navigation":157,"path":158,"seo":159,"stem":160,"tags":161,"__hash__":168},"blog\u002Fblog\u002Fwhy-plss-section-boundaries-are-not-all-640-acres-blm-survey-polygons-vs-estimated-centroids.md","Why PLSS Section Boundaries Are Not All 640 Acres: BLM Survey Polygons vs. Estimated Centroids",{"type":7,"value":8,"toc":140},"minimark",[9,13,16,21,30,38,42,45,48,51,54,58,61,64,68,76,79,102,106,109,137],[10,11,12],"p",{},"Most tools that convert a legal description to a location treat a section as a perfect 640-acre square. They estimate the center of the parcel from a grid formula, drop a pin, and call it done. For a lot of coarse work, that pin is close enough. The problem starts when you need a PLSS section boundary polygon for GIS work and you assume the polygon is a tidy box measuring one mile on each side. Many sections are not square, and a fair number are nowhere near 640 acres. If you build a boundary from grid math instead of the survey record, the edge you draw can sit hundreds of feet from where the parcel was actually surveyed.",[10,14,15],{},"This matters most to survey crews, GIS analysts, and anyone calculating acreage from a description. Here is why the 640-acre assumption breaks, and what a boundary drawn from BLM survey data gives you that a calculated centroid cannot.",[17,18,20],"h2",{"id":19},"the-640-acre-section-is-the-ideal-not-the-rule","The 640-acre section is the ideal, not the rule",[10,22,23,24,29],{},"The ",[25,26,28],"a",{"href":27},"\u002Fguides\u002Ftownship-range-system","Public Land Survey System"," starts from a clean idea. A township is a block six miles on each side, divided into 36 sections, and each section is one square mile, or 640 acres. Quarter it and you get four 160-acre quarter-sections. Quarter it again and you get 40-acre quarter-quarters. On paper, the grid is uniform.",[10,31,32,33,37],{},"The ground does not cooperate. Range lines run north along meridians, and meridians converge as they go north, so a township cannot stay a perfect square all the way up. The original survey instructions handled this by pushing the accumulated error into the north tier and the west tier of sections in each township. Those sections absorb the correction, which means the ",[25,34,36],{"href":35},"\u002Flearn\u002Fplss\u002Fsections","sections"," along the top and left edges of a township are rarely a clean 640 acres. The 34 interior sections come close to the ideal. The edge sections are where the arithmetic stops matching the map.",[17,39,41],{"id":40},"where-the-grid-breaks-government-lots-and-meander-lines","Where the grid breaks: government lots and meander lines",[10,43,44],{},"The survey did not force every irregular parcel into a quarter-quarter. Instead, it created government lots: numbered parcels used wherever a regular aliquot subdivision would not fit. You see them in two common situations.",[10,46,47],{},"The first is at the edge of a township. Section 6, in the northwest corner, is where most of the convergence correction lands, so it is commonly subdivided into government lots rather than regular quarter-quarters. A section like this can come in well under 640 acres, sometimes closer to 500, depending on how much correction the township carried.",[10,49,50],{},"The second is water. When the original crews reached a navigable river or a lake, they ran a meander line along the bank and stopped the regular subdivision there. The land between the meander line and the water was broken into fractional government lots that follow the shoreline. A section touching a river might carry Lot 1, Lot 2, and Lot 3 instead of a neat NE¼ and NW¼, and each lot is whatever size the survey measured it to be.",[10,52,53],{},"So a description like Lot 3 of Section 6, 4N 5E, Indian Meridian, Oklahoma, does not describe a 40-acre or 160-acre aliquot. It describes a specific surveyed parcel with its own shape and its own acreage. A grid formula has no way to know that. It will hand you a point as if the section were square, and for an irregular lot near a meander line, that point can fall in the wrong place entirely.",[17,55,57],{"id":56},"what-blm-survey-data-records-that-a-formula-cannot","What BLM survey data records that a formula cannot",[10,59,60],{},"The reason a boundary can be reconstructed at all is that the original General Land Office crews set physical corner monuments in the field and wrote down their positions. Those corners, not a grid equation, define where a section actually sits.",[10,62,63],{},"Township America resolves descriptions against official BLM survey data: the Geographic Coordinate Data Base (GCDB) and the CadNSDI cadastral layer. Both trace back to the surveyed corner record. A calculated centroid assumes a 640-acre square and reports the middle of that imaginary box. A boundary built from the corner record reports the parcel the survey actually established, including the edge sections and government lots that never fit the grid in the first place.",[17,65,67],{"id":66},"what-a-section-boundary-polygon-gives-you","What a section boundary polygon gives you",[10,69,70,71,75],{},"Instead of a single point, ",[25,72,74],{"href":73},"\u002Fguides\u002Fconvert-section-township-range-to-coordinates","polygon output"," returns the full boundary of the described parcel as a GeoJSON polygon: a closed ring of coordinates tracing the section or quarter-section as it was surveyed. Resolution runs across all 30 PLSS states and all 37 principal meridians, and it goes down to the 1\u002F256 aliquot part, which is 10 acres. For a government lot or a fractional section, the polygon reflects the real BLM survey boundary rather than a box inferred from grid math.",[10,77,78],{},"Three workflows show why that difference is worth caring about.",[80,81,82,90,96],"ul",{},[83,84,85,89],"li",{},[86,87,88],"strong",{},"Sending a crew to the right ground."," A field crew headed to a 40-acre quarter-quarter near a meander line needs the actual corner, not the center of an assumed square. The polygon puts the boundary where the survey put it, so the crew starts the day in the right parcel.",[83,91,92,95],{},[86,93,94],{},"Calculating acreage for a lease or appraisal."," If your acreage comes from assuming 640 acres per section, a fractional section overstates the tract. Measuring the mapped boundary, which reflects the BLM record rather than a fresh survey, gives you an area grounded in the actual parcel shape.",[83,97,98,101],{},[86,99,100],{},"Overlay analysis in GIS or CAD."," Checking whether a right-of-way crosses a section line, or whether a lease overlaps a surface tract, depends on the real edge. A polygon drops into QGIS or ArcGIS and behaves like any other layer.",[17,103,105],{"id":104},"getting-the-boundary","Getting the boundary",[10,107,108],{},"How you access the polygon depends on what you are doing with it.",[80,110,111,117,128],{},[83,112,113,116],{},[86,114,115],{},"Pro ($20\u002Fmo)"," shows the surveyed boundary on the map and adds boundary draw and PDF export, which covers spot-checks and field prep.",[83,118,119,122,123,127],{},[86,120,121],{},"Business ($40\u002Fmo per user)"," adds the structured ",[25,124,126],{"href":125},"\u002Fguides\u002Fdownload-results","exports"," a GIS or survey shop needs, including Shapefile, GeoJSON, and DXF, so the parcel goes straight into your GIS or CAD project.",[83,129,130,136],{},[86,131,23,132],{},[25,133,135],{"href":134},"\u002Fapi","API"," returns the same polygon geometry programmatically, for teams pulling boundaries into a pipeline rather than clicking through the app.",[10,138,139],{},"The takeaway is simple. A section is a legal unit, not a guaranteed 640-acre square, and the edge sections and government lots that break the grid are exactly the ones where a centroid estimate goes wrong. If your work depends on where the boundary actually runs, start from the survey record. Enter a description in Township America and read the boundary off the BLM data instead of trusting the grid to be square.",{"title":141,"searchDepth":142,"depth":142,"links":143},"",2,[144,145,146,147,148],{"id":19,"depth":142,"text":20},{"id":40,"depth":142,"text":41},{"id":56,"depth":142,"text":57},{"id":66,"depth":142,"text":67},{"id":104,"depth":142,"text":105},"\u002Fimages\u002Fblog\u002Fwhy-plss-section-boundaries-are-not-all-640-acres-blm-survey-polygons-vs-estimated-centroids\u002Fcover.webp","2026-08-05T10:00:00Z","A PLSS section boundary polygon from BLM survey data is not a 640-acre box. Here is why government lots and fractional sections break centroid estimates, and when the difference matters.",false,"md",{"author":155,"category":156},"Township America","industry",true,"\u002Fblog\u002Fwhy-plss-section-boundaries-are-not-all-640-acres-blm-survey-polygons-vs-estimated-centroids",{"title":5,"description":151},"blog\u002Fwhy-plss-section-boundaries-are-not-all-640-acres-blm-survey-polygons-vs-estimated-centroids",[162,163,164,165,166,167],"PLSS","GIS","Polygon","BLM","Surveying","GeoJSON","8kGgAm-ZdycmBW4exIkztbTbdCn6-c6Lt-f69wI1dWs"]