Metes-and-Bounds Survey Descriptions in GIS Mapping
My name is Chris Mumford and I have been a user of the desktop TatukGIS Editor since August 2011. In 2016 I contributed feedback about the usefulness of the Editor in my real estate appraisal business here in New Hampshire. In the following narrative, which is composed of four sections, I will begin with a brief review of the strengths and shortcomings of the metes-and-bounds property description as is commonly encountered in New England and many other areas of the United States. Then I will expand into the process I have developed for employing TatukGIS Editor to convert a metes-and-bound property description into a geo-referenced GIS polygon.
Part 1: Introduction to Use of Metes-and-Bounds Descriptions in GIS Mapping
As a matter of introduction, a metes-and-bounds description begins at a given point on a property boundary and then follows a step-by-step series of “calls”, i.e., recitations of bearing and distance, that trace the boundary line around the perimeter of the property and back to the point of its beginning. Here in New England, some properties are still described by an archaic style of metes-and-bounds description in which the calls reference long-lost physical features and neighboring landowners. For example, the recorded deed for the May 2023 sale of a heavily forested woodlot located in my town contained the following metes-and-bounds description:
Though not nearly so evocative of “old times,” most contemporary metes-and-bounds descriptions are based on a professional survey in which bearings have been taken in degrees, minutes and seconds, and distances measured to one-hundredth of a foot. The following excerpt from a recently recorded deed is a good example of such a high-precision metes-and-bound description:
From the perspective of the surveyor and landowner, the fundamental task of a boundary survey is to identify and/or establish physical monumentation around the perimeter of a given property and then document the entire process with a plan. For a variety of reasons relating to practical, legal, and traditional aspects of the surveying profession in northern New England, however, the bearings created in such a process are typically magnetic rather than true north, and boundary points are seldom geo-referenced.
From the perspective of GIS practitioners, on the other hand, a modern metes-and-bounds property description is the authoritative data source that may be used to precisely define the polygonal shape of a given property. If, however, the survey is based on compass bearings—as is likely— the metes-and-bounds description does not address the equally important aspect of the property’s physical orientation. Further, if the survey does not include at least two geo-referenced corners along the boundary—as is likely—the property’s precise location on the surface of the earth is a second unknown factor.
Practically speaking, the GIS practitioner faces multiple challenges when attempting to use a metes-and-bounds description: 1) How to efficiently and accurately capture the bearing and distance data conveyed by the “calls” and 2) How best to geo-reference the polygon to a coordinate system, and where necessary, align or rotate the shape to 'true north'.
Part 2: Creating a High-accuracy Polygon in the Editor
We will next explore a method for using the Editor to create a high-accuracy GIS polygon from a survey. The following narrative will take the reader through the creation of a polygon with a geo-referenced starting point and compass bearings.
In the initial step of the process, we will first examine the relevant portion of the survey, as shown below with the parcel highlighted in yellow. Recalling that the survey is not geo-referenced, our immediate objective is to identify at least one discernible “point feature” along the perimeter of the boundary that can be readily observed in GIS imagery (as visualized in Editor) and from which its X-Y coordinate may then become the geo-referenced starting point for the metes-and-bounds “calls.” In so doing and after close scrutiny of the survey, I would conclude that the most likely observable “point feature” is the corner of the stone wall (inside the black circle in the following image) along the parcel’s southwest boundary line.
In the next step we use the Editor to view the approximate survey area by means of two different streaming imagery services [aka ‘WMS' (Web Map Service) layers], one providing ortho-quality aerial imagery and the other LiDAR DEM data, made available through NH GRANIT (the New Hampshire statewide GIS clearinghouse). A WMS layer is opened in the Editor by clicking on the Layer menu option and selecting Open from server, which opens the Open from web service dialog box that allows entering the WMS layer's URL address.
To ensure the WMS layer, and any layers opened with it, are displayed in the desired coordinate system, it is appropriate to make a coordinate system selection for the map project. This is done by clicking on the File menu option and selecting Coordinate Systems to open the Coordinate System dialog box, as pictured below. Within this dialog box, the coordinate system can be selected from a drop-down list. My preferred coordinate system is ‘NAD83 New Hampshire ftUS – epsg:3437’, also known as the New Hampshire State Plane coordinate system. Importantly, this coordinate system reflects feet distance units, the same units as the mete-and-bounds survey calls, which ensures a polygon created from the survey calls will correctly scale to the WMS layer.
Turning first to the 2021 aerial imagery, as shown below, the “stone wall corner” is not visible due to the prevalence of coniferous trees.
Turning next to the LiDAR layer pictured below, the corner of the stone wall is immediately discernible. We will, therefore, use this as the base layer.
In summary, we first examined the survey and found a likely starting point (the stone wall corner). We then used the Editor to observe the survey area by means of multiple types of georeferenced imagery and, in so doing, positively identified the GIS coordinates of the stone wall corner.
The next major step of my preferred ‘polygon creation process’ involves use of an Excel spreadsheet to which I first manually enter the co-ordinates of the starting point followed by manual entry of each metes-and-bounds “call” as read off the survey. The spreadsheet, shown below, creates the grey-shaded column of data points which is specially formatted for use in the Editor. After copying the column to the Editor's Clipboard, the Editor may then be prompted to automatically read the Clipboard and create the desired GIS polygon.
Detailed steps are as follows:
I. Collect X-Y Co-ordinates of Starting Point in Editor:
- Use the Editor Select Localize feature to hover the ‘fingertip’ over the desired starting point feature (as seen in the imagery), then right-click Copy Coordinates to Clipboard...Map Units.
II. Create formatted data points in Excel spreadsheet, shown below:
- Paste the X-Y co-ordinates of the starting point into indicated cells.
- Enter each metes-and-bounds “call” in appropriate cells at left side of spreadsheet.
- Set up necessary formatting for Editor in Column T.
- Copy grey-shaded area.
III. Create polygon in Editor using same project from which starting point co-ordinates were found and copied.
- From the Layer menu option, create a New Temporary Layer.
- In the menu bar, select the Polygon digitizing option:
- From the menu bar, select “Shape...Import shape from...” which will open the following pop-up window:
- Click Import and the Editor will automatically create the unaligned “compass bearing” polygon:
At this stage, the Editor's area measurement tool can be used to determine, or verify, the acreage of the property parcel by calculating the area of the GIS polygon.
Note 1: The process described above purposefully excludes the survey’s last ‘call’ from the data copied to the Clipboard for use by Editor in creating the polygon. Doing so assures ‘closure’ but assumes 1) the user has correctly entered all data points into the spreadsheet with no transcription errors and 2) the survey calls are factually correct. Neither assumption is necessarily true. Therefore, it is recommended to test the accuracy by initially also including/copying the final survey ‘call’ into the Clipboard during the process of creating the polygon. Because there is nearly always a small property description closure error and a GIS polygon must always close, this step will force the Editor to add an additional edge (hopefully a small one) to close the polygon. This polygon 'closure edge' will run between the final vertex created by inclusion of the final survey 'call' and the starting vertex (0). The length of the 'closure edge' allows the user to visually ascertain the degree of closure error. If the closure error is a matter of inches or a few feet, this indicates i) an acceptably small cumulative error and ii) the data points for each call are almost certainly correct.
As pictured below, at close zoom level we see the closure error of our polygon is less than an inch (shown by the length of the polygon edge between vertex 9 and the starting vertex 0). The 'calls' and resulting polygon are deemed excellent.
Upon achieving acceptable closure, the user may elect to i) leave the final 'closure edge' in place to document the error or ii) opt for a smoother appearance by removing the ‘closure edge’ created by inclusion of the final survey call. This can be done by simply deleting the final (i.e., highest numbered) vertex from the polygon.
If the closure error is suspect, however, the user should reexamine all entered data points, one or several of which may have been incorrectly entered. On rare occasions the user may even find an error in one of the line calls recorded in the property deed description, perhaps made in the process of transcribing the survey data to the deed record.
Note 2. The bearing and distance data could also be used to initially create a vector polyline shape instead of a polygon, which might be more illustrative. Unlike with the polygon, the degree of non-closure using a line will be represented by a physical gap between the line's starting point vertex and the ending vertex. As discussed above, the size of the gap indicates whether the closure editor is acceptable or the data should be reexamined for accuracy. The Editor Create Polygon command can be used to then convert the line shape into a polygon shape.
Part 3: Using the Editor's COGO Feature
In the previous section we created a high-accuracy polygon with compass bearings. The following narrative will take the reader through the process of rotating the polygon to 'true north' bearings.
I. Determine survey declination.
- Returning to the survey that was used in the previous section, further examination of its ‘north arrow' symbol indicates the survey bearings are “Magnetic Jan 02.”
- The US National Oceanic and Atmospheric Administration offers a very good ‘Magnetic Field Calculator’ [MFC] which may be found at: https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#declination
- As shown in the following compilation of screenshots, the user must step through the MFC prompts for 1) location, entered here as a Zip Code, and 2) preferred date, in this case January 2002. Upon entry, the calculator returns a pop-up message stating that the magnetic declination is 15° 24' W. This value must be re-stated in decimal degrees as –15.40° = [15 + (24/60 * –1)] for subsequent use in the Editor.
II. Edit polygon using the Editor's COGO feature
As a matter of introduction, the Editor offers an outstanding COGO (coordinate geometry) feature that enables GIS users to precisely digitize and edit vector data.
- Turning now to the task of rotating our polygon to the degree indicated by the NOAA Magnetic Field Calculator, we begin in the Editor by 1) selecting the relevant polygon layer, 2) clicking the Edit shape icon in the toolbar, and 3) clicking on the polygon itself in the main map panel. Doing so not only reveals the polygon vertices but also opens the Selected panel with the bearings of each vertex, as seen in the following screenshot:
- At the bottom of the Selected panel as depicted below, 1) click on the COGO-360 tab, 2) widen the Bearing and Distance columns (if desired), and 3) select Relational from the drop-down list box in the Bearing column.
- Note that only the bearings shown in Rows 2-8 are relational values whereas the bearing shown in Row 1 (i.e., the first call from the starting point) is always the absolute value. Converting the polygon’s bearings from “Magnetic Jan 02” to “true north” is thus a matter of manually updating the value in the first row to 293.71 [= 309.114 – 15.4]. Do NOT, however, change any values in subsequent rows because the Editor, by virtue of the Relational bearing setting, will automatically perform all necessary ‘coordinate geometry’ steps in the process of realigning the X-Y vector data in Rows 2-8.
- Clicking the OK button at the bottom of the Selected panel rotates the polygon around vertex 0 (the starting point at the ‘stone wall corner’), as shown below:
- In the final step, we end the editing session for the polygon and turn on the base layer. As shown below, the polygon now appears to align nicely with the stone wall originally seen in the LiDAR imagery. Mission complete!
- As a final comment, the reader is again reminded that the above-described method will accurately reproduce the given parcel’s shape and size as described in metes-and-bounds calls taken from a survey. Said method does not, however, necessarily arrive at a “survey grade” location and alignment for the given parcel.
If the layer containing the drawn polygon is saved, it will be saved georeferenced to the project (i.e., display) coordinate system, in this case NAD83 New Hampshire ftUS - epsg:3437.
Part 4: Alternate Approaches to Creating a High-accuracy Polygon with Editor’s COGO Feature
Earlier sections examined use of the Editor in a multi-step process for creating a high-accuracy geo-referenced GIS polygon from a property's metes-and-bounds description. This post will examine several alternate methods for achieving the same general objective, i.e., the creation of an accurate parcel shape within the user’s GIS mapping system.
I. 'Manual use of the COGO feature
- A property boundary is fundamentally a connected series of line segments, each defining an 'edge' of the resulting GIS polygon. As previously discussed, a metes-and-bounds boundary description begins at the starting point of a given segment and then progressively ‘calls’ or defines each successive line segment on the basis of its bearing and length. Not yet discussed is the fact that such a “progressive” boundary description may proceed in either a clockwise or counter-clockwise fashion, hence the unique nomenclature of the metes-and-bounds ‘call.’ For example, “S 30° 45' 22″ W 100 feet” could be used to describe a given line segment in a ‘clockwise’ boundary description, and “N 30° 45' 22″ E 100 feet” would be used to describe the exact same line segment in the reverse or counterclockwise boundary description. So described, the absolute bearings of the two lines are ±180 degrees apart from one another. As a general rule, ‘N...E’ is opposite ‘S...W’ and ‘N...W’ is opposite ‘S...E.’
- A metes-and-bounds ‘call’ must be converted to its absolute bearing before use in Editor’s COGO feature. Doing so is a two-step process:
- First, mathematically convert the ‘degrees / minutes / seconds’ format to its decimal degree [DD] equivalent with the following calculation:
Decimal Degrees [DD] = Degrees + (Minutes / 60) + (Seconds / 3,600)
- Next, determine the orientation of the given call and adjust its DD by means of the following table in arriving at the absolute bearing:
= 360 – DD
= 0 + DD
= 180 + DD
= 180 – DD
- Example 1: The absolute bearing of S 30° 45' 22″ W would be calculated as follows:
- Step 1: DD = 30 + 45/60 + 22/3600 = 30.756111
- Step 2: The ‘call’ used in the example has a ‘S...W’ orientation, and therefore its absolute bearing is 210.756111 degrees. [ = 180 + 30.756111]
- Example 2: The absolute bearing of N 30° 45' 22″ E would be calculated as follows:
- Step 1: DD = 30 + 45/60 + 22/3600 = 30.756111.
- Step 2: The ‘call’ used in the example has a ‘N...E’ orientation, and therefore its absolute bearing is 30.756111 degrees. [ = 0 + 30.756111]
- Applying the above-described calculations to the relative bearings in the same metes-and-bounds calls that were used in the earlier posts, we arrive at the following table of absolute bearings.
|N 50 53 10 W
N 50 43 17 E
S 36 11 54 E
N 73 34 40 E
N 50 56 15 E
S 19 18 35 E
S 49 13 15 W
S 71 49 50 W
N 50 53 10 W
- In the Editor, create a temporary layer [Layer...New Temporary Layer], click the Polygon icon in the ribbon, hover the “Digitizing pointer hand’ over the desired starting point (for example, the inner corner of the stone wall), and then left-click to establish the ‘X Y’ starting point.
- Click on the COGO-360 tab in the Selected panel, enter the absolute bearing and distance of call #1, then click the OK button:
- In the Selected panel, change the Bearing from absolute to relational and enter the absolute bearings and distances of calls #2-8. Click the OK button to render the completed polygon:
- The completed polygon is oriented to its compass bearing. In Part #3, the magnetic declination was determined by the age of the survey, which informed the necessary degree of rotation to bring the polygon into alignment with ‘true north.’ In this example, however, we will examine the first of two alternate methods of aligning the polygon.
- As stated on the original survey, the first call should align with the stone wall that is evident in the LiDAR imagery. To find the orientation of this wall, we simply create a line feature on the wall in our Temporary layer and read/copy its bearing in the COGO-360 panel, i.e., 293.5664978.
- Next, select the polygon with the Edit tool, change Bearing from absolute to relational in the Selected panel, and enter 293.5664978 into the Bearing column of the first row. Click OK to rotate the polygon to the same orientation as the line to arrive at the 'true north' orientation.
- The second alternate method of rotating the polygon into proper alignment is use the Rotate Shape tool, which can rotate a shape around one of its vertices or its centroid. (Rotate Shape is one of several special purpose Editor scripts found under the Edit menu at Tools...Tool Manager...). Here we want to rotate the polygon on its starting vertex (i.e., ‘Part 0, Index 0'). The tool allows for rotations in increments of 1 degree, so we select 15 degrees and click Rotate button to achieve the desired effect.
II. Additional comments
The following points with respect to Editor coordinate system functionality are useful to know:
- The coordinate system conversion (reprojection) feature allows a layer georeferenced to any coordinate system to be opened and readily viewed together with map layers in any other coordinate system(s). As required, the Editor reprojects the presentation of each layer to the display (i.e., project) coordinate system.
- If a project coordinate system is not specified by the user, the coordinate system of the first-opened layer becomes the project coordinate system, which governs the display of subsequently opened and any newly created layers.
- Upon saving, a newly digitized layer will be saved georeferenced to the project coordinate system (unless the user selects a different coordinate system during saving).
- The Editor supports thousands of coordinate systems. A helpful built-in search tool enables finding a coordinate system from the list by entering just a few characters from its name, such as "New Hamp" or "3437".
This concludes my discussion about use of the TatukGIS Editor in creating high-accuracy georeferenced parcel shapes. A future post will examine my use of the Editor to create slope maps from a LiDAR Digital Elevation Model in support of ‘Highest & Best Use’ property appraisal analyses.