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Horizontal Control Network (Monuments)
The horizontal control network is comprised mostly of section and 1/4 section corner markers throughout the county. These locations were first determined as a result of the nationwide PLSS (Public Land Survey System) Program, which was a cornerstone to the Federal Land Grant Program in the mid 1800s. The PLSS was intended to simplify the defining and documenting of land ownership in the handover of federal lands to private ownership. At the time, the corners were marked with a variety of things, including stones, spikes, iron posts or nails in pavement.
From 1979 to 1984, DuPage County initiated a county-wide re-monumentation program with specific objectives. Questionable corner markers were replaced with more durable and permanent monuments, mostly Harrison Ferro-Magnetic Survey Monuments that still exist today. And most importantly, for the first time the DuPage County PLSS was spatially referenced to the NGS (National Geodetic Survey) control network. Prior to this, there had been no coordinates assigned to the section corners. The level of precision is less than 1 ft variance for every 20,000 ft traveled, or second order class II.
Vertical Control Network DuPage County (Benchmarks)
The current DuPage County network of vertical control marks was established primarily between the years 1983-86. The leveling work was contracted to Marchese and Sons, Inc. of Roselle, Illinois. All level runs were specified to meet the National Geodetic Survey (NGS) Second Order, Class Two level run requirements, and all runs began and ended on what was then classified by NGS as a First Order vertical control point.
The first run completed on this project was submitted to NGS in Blue Book form, and was accepted by NGS and included in the NGS database for readjustment to the NAVD of 1988 (see attached .pdf NGS letter). The purpose of this submittal to NGS was to receive acceptance of our methodology. Subsequent level runs were not submitted to NGS due to budgetary constraints.
During the 1988 NAVD readjustment, NGS downgraded a number of the First Order vertical control points we had used as the start/end points of our level runs. As a result, the run we had submitted to them was reclassified to Third Order in the NAVD 88 database.
NGS Control Network
Today, the NGS is the premier federal agency providing the public with survey control information. The DuPage County network is referenced to the NGS network and positions were established according to NGS guidelines. Surveyors working in DuPage County may tie to either NGS or DuPage benchmarks or monuments. In fact, several DuPage benchmarks are considered part of the NGS network.
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