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Land Surveys Frequently Asked Questions

Q. There are surveyors on my property. Why are they there?

A
. If they are Baltimore County Surveyors they should have given you a letter explaining their presence. If they are from a private surveying firm, you will need to ask them directly. Baltimore County does not regulate the many surveying companies operating in the County.

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Q. I want to put up a fence or I am having problems with my neighbors. Will Baltimore County survey my property?

A.
Baltimore County does not do surveys for private citizens. You can look in the yellow pages under "Surveyors - Land" or visit the Maryland Society of Surveyors to find surveyors in your area.

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Q. Someone has put paint marks in the street in front of my property. What is going on?

A.
Paint marks in the street or on a sidewalk are usually preceded by some sort of construction in the area. This could be work being done by BGE, Verizon, Comcast, or some other utility or construction company. You could call Construction Contracts Administration at 410-887-3451 to see if it is a Baltimore County job. We would not have information if it is another company.

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Q. I am working on a project in Baltimore County. How do I find out if there is any existing County control nearby?

A.
This information is available online, to subscribers, through Survey Control. You can also fax or email us a map, showing your site, and we will check our records for the appropriate data. We will fax or email the information back to you, or you can come to our office to pickup the data. We will not read survey control data over the telephone.

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Q. How can I get current Continuously Operating Reference (CORS) information for Baltimore County?

A. The Baltimore County CORS, known as BACO, is part of the National CORS network. The National Geodetic Survey CORS web site maintains five second epoch data from station BACO. Type in BACO in the Enter Site ID box for more information. The Baltimore County Land Survey Division maintains one second epoch data for a period of 60 days. Call 410-887-3540 for information about the one second data

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Q. Where can I go to complain about a private surveyor?

A. The Maryland Department of Labor, Licensing and Regulation will investigate complaints and take any appropriate action.

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Q. How many feet different, is it between the old county vertical datum (BCD) and the new one (NAVD 88)?

A. Due to the differences in the ways the two systems were established, as well as other factors, there is no survey grade conversion that can be applied to convert from one system to another. Where we have established NAVD 88 elevations on the older BCD benchmarks and found differences ranging between 1.5 to 1.9 feet. Based on our observations Baltimore County uses 1.7 feet as the approximate difference between the two systems. A benchmark with a BCD elevation of 100 feet would have an approximate NAVD 88 elevation of 98.3 feet.

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Q. What is the relationship between a geodetic vertical datum, such as Baltimore County Datum (BCD), National Geodetic Vertical Datum of 1929 (NGVD29) or North American Vertical Datum of 1988 (NAVD 88), with the various water level/tidal datums (mean low water, mean sea level, mean high tide etc.)?

A. Tidal levels, such as high tide, low tide, mean tide and others, are typically defined as the average of a 19-year period known as a tidal epoch. These water surface levels are unique to a particular site along the waterway and will not be constant along the entire length of a waterway.  Many local, state, and national agencies have created fixed vertical (elevation) datums such as BCD, NGVD 29, and NAVD88 for use in surveying and engineering design. These fixed datums were originally based on water surface measurements at one or more tidal stations and may even use a water or tidal term (sea level datum or mean low tide) for the zero elevation of that fixed vertical datum. The fixed vertical datums are as the name implies "fixed" in times as the date they are created with some of them created over 100 years ago. The elevations of the fixed datums are not revised or updated when every new 19-year tidal epoch is released. Some of the fixed datums do not factor in the differences in gravity and the other forces defining an equipotential surface. Any relationship with water surface or tidal level that may have existed when the datum was first established no longer exists today so there is not relationship between fixed datums and water level or tidal datums.

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Q. I am preparing an application for waterfront construction and the requirements refer to restrictions from mean low tide. What elevation is mean low tide?

A. The relationship between geodetic vertical datum and water or tidal datum applies, but there is an exception in this situation. When working in Baltimore County, the Baltimore County Zoning Regulations, section 417 'Waterfront Construction' provides the information to answer this question. It states "... mean low tide as prescribed in the Baltimore County Design Manual..." The current version of the Baltimore County Design manual was adopted on August 2, 2010 and includes Plate SU-2 (Chart of Datums) in the Land Surveys Section. On Plate SU-2 mean low tide is set as zero datum. While the term mean low tide can be a water or tidal level, in the case of the Baltimore County Zoning Regulations, it defines mean low tide as a fixed elevation. When dealing with Baltimore County Zoning permits for waterfront construction, the mean low tide elevation is 0.0 feet as referred to in the old Baltimore County Datum elevation system.

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Revised August 8, 2013

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