WhiteStar Lots and Tracts coverage is growing by leaps and bounds (perhaps we should say metes and bounds!). And this question pops up ever more frequently in conversation – what exactly is the difference between lots and tracts and parcel data? So we thought we’d take a little time here to walk through it.
You’re likely intimately familiar with the standard public land survey model of a square township, divided into 36 neat sections. And as you probably also know, once the surveyors of yore headed out into the field to apply that model on the ground, it pretty much never produces 36 perfectly equal, nicely square sections. The ground measurements would generally come up a little short or long, usually on the north and west sides of the township. Where that has the most effect is when you get down to the quarter-quarter level, where a purely mathematical division into four would produce rather wonky results. And so the non-conforming quarter-quarter was replaced by a “lot”, where we assume that the land boundary will deviate substantially from a standard survey grid division.
Another situation that wreaks havoc with the township model is navigable waterways. A river meandering through a gridded township could produce a land parcel that lay 98% on one side of the river, with a tiny 2% sliver on the other side. And since rivers also move with time, that land might eventually cease to exist entirely. And so allowances are made, and the boundaries are defined respecting waterways, sometimes maintaining the township grid model but clipping a square boundary with an irregular edge following the path of the river, and sometimes creating riverfront lots that don’t follow the township model at all.
Lots are generally somewhat organized in layout – like the two examples above. Then we have tracts, which is a sort of a catchall category for lands that don’t fall nicely within that organized system. Here we’ll see lands like Indian reservations, mining claims, and other sorts of irregularly defined lands.
In all of these cases, newer surveys respect older ones, and so all of these quite different boundaries ultimately end up pieced together – sometimes nicely, and sometimes more like a Paul Klee abstract painting. The point is that irregular lots (and the rest of the survey) are part of the original land survey, and they are static. They were created by the General Land Office, or the Bureau of Land Management, and they are legally mandated – they don’t change.
A parcel, on the other hand, is a much more dynamic creature. The most important thing to understand about a parcel is that it is derived from the boundaries of the survey we’ve been talking about above – a lot could be subdivided, ownership changes – but it doesn’t change the survey. It references the survey, and may be described using the survey, but it isn’t the official survey. A parcel is a derivative of the survey, and is of course the source of real estate information, but has no standing in the public land survey system.
And so it’s important to understand, when you’re working with land grid, what’s an official source and what isn’t – and in the case of lot and tract boundaries, the GLO and BLM lots and tracts that WhiteStar Lots and Tracts is based upon is the authoritative source for where the edge of a piece of land is.
If you’d like to take a first hand look at it, we’ll be in Houston March 18th through 20th – give us a call or email firstname.lastname@example.org to arrange a demo.
March Events - Houston and Palm Springs
The Petroleum GIS Breakfast with Bryan Ferguson
The Petroleum Club of Houston
Monday, March 18th – 8:30 am to 10:30 am
Join Eagle Information Mapping, Hart Energy, and WhiteStar for a complimentary breakfast and guest speaker Bryan Ferguson, GIS Data Manager for BP Biofuels in Houston as he presents lessons learned in implementing a cloud-based GIS system.
Get more information and register for this free event!
Esri Partner Conference
Palm Springs Convention Center
March 23rd to 26th, 2013
Visit our booth at the GIS Solutions Expo on Monday March 25th
Get more conference information here.