Surface parcels to net mineral acres — the data layer every Texas mineral valuation depends on

Before anyone can value a Texas mineral interest, two boring-sounding numbers have to be defensible: how big is the surface tract, and what fraction of the minerals beneath it does your client own? Both have well-understood failure modes that quietly destroy every downstream number in the valuation. This post walks through both, with the math, the data sources, and the eight-line audit any pipeline should run before a decimal interest or NPV gets calculated.

This is Stage 1 and Stage 2 of the five-stage mineral valuation pipeline. The anchor post covers why the pipeline matters and where allocation wells fit; this one is the data layer everything else gets built on.

Stage 1 — From an address to defensible surface acres

Input: an address, an APN (assessor parcel number), a latitude/longitude pair, or a county shapefile
Output: a parcel polygon (typically GeoJSON), a surface acreage figure, and a confidence score

Three things matter here, and each one is a known source of expensive error:

1. Use the correct unit conversion

One acre is 43,560 square feet. Not 43,360. The latter is a surprisingly common typo in field spreadsheets, and it propagates through every subsequent calculation — a 160-acre tract reads as 160.74 acres if you started with the wrong constant. Build it as a constant in a config file, not as a number people retype.

Other useful conversions for the pipeline:

• 1 acre = 43,560 sq ft = 4,046.86 sq m = 0.4047 hectares
• 1 section (PLSS) = 640 acres = 1 sq mile
• 1 township (PLSS) = 36 sections = 23,040 acres

2. Use geodesic area or an equal-area projection — never Web Mercator

This is the single most common failure mode in software-built mineral pipelines, including some that are sold commercially. The Web Mercator projection (EPSG:3857), which Google Maps and most consumer web maps use, distorts area badly. The further you get from the equator, the worse the distortion: at the latitude of West Texas (~31°N), Web Mercator overstates area by about 15%. A 160-acre tract on the ground reads as ~184 acres if you compute its area in Web Mercator coordinates.

For a Texas mineral pipeline:

• Compute area geodesically (PostGIS: ST_Area(geometry::geography)) — handles the curvature directly
• Or reproject to an equal-area projection before computing area: EPSG:6580 (NAD83(2011) / Texas Centric Albers Equal Area) is the canonical Texas equal-area projection. EPSG:5070 (CONUS Albers Equal Area) is a defensible fallback for multi-state work

The cheapest fix for legacy pipelines is to add a single PostGIS check at parcel ingestion that compares the Web Mercator area against the geodesic area, and flags any parcel where the two differ by more than a few percent. If the parcel was drawn or computed in Web Mercator, this check catches it immediately.

3. Track confidence by data source

Not all parcel data is created equal. The downstream valuation should inherit the uncertainty of the input parcel, which means the data source has to be tracked, not just the polygon.

Texas priority county GIS endpoints

If you're standing up a Texas mineral pipeline, prioritize the active-basin counties first. These produce the bulk of the modern horizontal-well activity and account for the majority of recent permit volume:

• Delaware Basin (west): Reeves, Loving, Culberson, Ward, Pecos. Add Eddy County, NM if any acreage crosses the state line.
• Midland Basin (east): Midland, Martin, Howard, Glasscock, Andrews, Upton.
• Eagle Ford: Karnes, DeWitt, McMullen, La Salle, Dimmit.

Most of these counties expose their GIS as ArcGIS REST endpoints, which are straightforward to ingest into PostGIS with ogr2ogr on a nightly schedule.

Stage 2 — From a surface parcel to net mineral acres

Input: a parcel polygon plus the chain of title documents
Output: the Undivided Mineral Interest (UMI), the Net Mineral Acres (NMA), and the mineral tract polygon

Texas defaults to severed mineral estates

The single most important fact for Texas mineral work: the surface estate and the mineral estate are routinely held by different parties. When a surface parcel was sold somewhere in the chain of title, the seller may have reserved the minerals entirely, reserved a fraction, or deeded them off separately years before. The mineral interest does not equal the surface acreage by default.

This is why a "160-acre tract" might have a current mineral owner who only holds 60 net mineral acres — even though the surface boundary is unchanged. The mineral chain runs in parallel with the surface chain, with its own conveyances, reservations, and partitions.

UMI and NMA math

The relationship is straightforward arithmetic once the UMI is known:

NMA = surface_acres × UMI

The hard part is determining the UMI. UMI changes every time the minerals are sold, partitioned, leased back, or inherited. A realistic chain looks like this:

Surface parcel:                                160 acres

1962 deed: grantor reserves 1/2 mineral interest
          → mineral estate split: grantor 50% / new owner 50%

1988 deed: subsequent owner retains 1/4 of his 1/2 interest
          → that owner now holds: 1/2 × (1 − 1/4) = 3/8 UMI

Current owner's UMI: 3/8 = 0.375
NMA = 160 × 0.375 = 60 net mineral acres

That 60 NMA is the number every downstream stage of the valuation depends on. Get it wrong and everything else is wrong by the same percentage.

UMI tracking is a discipline, not a number

UMI changes over time, and the source of any UMI assertion matters because different sources have different evidentiary weight. A defensible pipeline tracks UMI alongside its source:

• Mineral title opinion from an oil and gas attorney — highest weight. Authoritative for the date it was rendered.
• Operator division order — the UMI the operator has formally accepted and is paying against. High weight, but operator division orders contain errors at non-trivial rates.
• Owner attestation (e.g. self-reported in an intake form) — useful starting point; needs verification.
• Estimated from deed records — defensible for triage and screening; not authoritative.

When two sources disagree — for example, a 0.50 division order interest against a 0.625 UMI in your records — the pipeline should flag the delta for human review rather than silently resolving in either direction. That single rule is the most valuable mineral-audit feature most calculators don't have.

Data sources for mineral ownership

No automated pipeline replaces a mineral title opinion for high-value transactions — the attorney work product carries evidentiary weight that no software does. What an automated pipeline can do is cache the underlying records, surface conflicting UMI assertions, track UMI over time, and dramatically reduce the per-tract title opinion volume by handling triage and pre-screening.

Edge cases worth knowing about

A handful of mineral interest variants behave differently from the simple "owner of N acres" model:

• Mineral interest on a different tract boundary than the surface — common after partition or aggregation. The mineral tract polygon and the surface parcel polygon are not the same shape.
• Royalty interest vs. mineral interest — a pure royalty interest holder has no executive rights (cannot sign new leases, cannot pool, cannot grant access). They still receive their share of production once leased, and the NPV math works the same — but the legal status is different.
• Term interests — minerals that revert to the original grantor after a defined period of non-production (commonly 10 or 20 years). Material for valuation if production is intermittent or pending.
• Non-participating royalty interests (NPRI) — receive a share of production but no signing bonus, no delay rentals, and no surface payments.
• Working interest reservation — sometimes a surface seller reserves a working interest alongside or instead of a royalty interest. Different math entirely; not the subject of this pipeline.

An 8-line audit for Stages 1 and 2

Run any Texas mineral parcel + ownership intake through this checklist before passing it downstream:

1. ☐ 43,560 sq ft per acre used everywhere (not 43,360)
2. ☐ Geodesic area or equal-area projection used for surface acreage — never Web Mercator
3. ☐ Source tier tracked per parcel (county GIS / aggregator / user-drawn)
4. ☐ Web Mercator vs geodesic area check raises a flag if the two differ by more than 2%
5. ☐ NMA = surface_acres × UMI computed explicitly — never assume NMA = surface acres
6. ☐ UMI assertions tracked alongside source (title opinion / division order / owner attestation / estimate)
7. ☐ Mineral tract polygon distinct from surface parcel polygon where they differ after partition or aggregation
8. ☐ Audit log: every NMA record links back to its source documents

A few terms worth knowing

The takeaway

Stages 1 and 2 of the mineral valuation pipeline are unglamorous. They're acreage computation and ownership chain tracking — which sounds like the most boring part of a mineral pipeline, and is in fact where the most expensive errors hide. A 15% Web Mercator distortion at Stage 1 propagates as a 15% error into every NPV downstream. An undetected UMI miscount at Stage 2 produces a decimal interest that won't match the operator's division order — and the gap surfaces six months later when the first royalty check is wrong.

The audit checklist above catches the recurring failure modes. Every line on it exists because someone, somewhere, shipped a valuation built on a wrong number at one of these stages. Get the data layer right and the rest of the pipeline becomes interpretable. Get it wrong and no amount of decimal-interest sophistication downstream will save the answer.

The next stages handle the well-side of the calculation: classifying every well that intersects the tract, and computing the decimal interest correctly per well type. That's covered in the decimal-interest math post, which is also where the allocation-well wrinkle from the anchor post gets fully worked out with math.

Sources

• PostGIS — ST_Area documentation (geodesic and projected variants)
• EPSG:6580 — NAD83(2011) Texas Centric Albers Equal Area
• EPSG:5070 — CONUS Albers Equal Area
• Texas Railroad Commission — Drilling Permits and GIS Portal
• Texas General Land Office — state-owned mineral records
• National Association of Division Order Analysts (NADOA) — model division order standards
• Texas Land Title Association — mineral title opinion practice standards

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