BG-Map
Getting Started in Computerized Mapping for Arboreta and Botanical Gardens

by Mark Glicksman

Also See:
Notes and Suggestions for Botanical Garden Surveyors

By Walt Dunlap and Wayne Cahilly, Institutional Mapping Department, The New York Botanical Garden


 

Setting Up a Coordinate System

Establishing a Grid

Placing Markers

Creating a Basemap

 

Getting started in computerized mapping may seem a daunting prospect. With so many choices to be made in hardware and software, it's easy to lose sight of some of the first and most basic tasks in setting up any mapping system - creating a grid and a basemap. This article is intended to shed some light on this subject.

Once you have established a grid, placed markers, and created a basemap, you are ready to purchase hardware and software, survey plant locations, and begin implementation of your computerized mapping system.


 

 Setting Up a Plane Coordinate System


In order to define the locations of plants on your computerized map, it is necessary to set up a coordinate system. Each plant will have associated with it a unique x coordinate and a unique y coordinate that exactly specify its position.

In surveying terms, this is considered to be a plane coordinate system because it represents the surface of the earth as a flat surface. Thus, you need not be concerned with the curvature of the earth or changes in elevation when defining the locations of plants. All you need to know are their x and y coordinates.

If possible, the coordinate system should be referenced or "tied into" a standard plane coordinate system for your locality. In the United States, each state and the District of Columbia has established its own plane coordinate system. By referencing a local plane coordinate system, you will be able to easily utilize survey data gathered by GPS equipment and by surveyors or engineers who perform work on your property. And, you will be able to use other data that may be available to you, such as a digital elevation model (DEM).

Establishing a Local Coordinate System with an Arbitrary 0,0 Point

A point on your property that would correspond to the lower leftmost corner of the map can be arbitrarily established as having coordinates 0,0. All other points on the property can then be referenced to this point. The coordinate system is usually aligned so that the x-axis runs east and west and the y-axis runs north and south. This is desirable but not essential.

Using State Plane Coordinates Directly

Or, you can choose to use State Plane Coordinates directly, eliminating the need to perform a coordinates conversion when using survey data from other sources. The only disadvantage of doing this is the large 6 or 7 digit numbers that you will be working with, as opposed to 4 or 5 digit numbers for a local coordinate system,

 


 

Establishing a Grid

 

Unless a property is very small, for ease of mapping, it will be necessary to subdivide it into smaller, more manageable mapping units or chunks. This is called establishing a grid.

If you look at a road map, you will notice that it is divided into a number of squares. The squares along the bottom of the page may be labeled with letters, and the squares along the side of the page may be labeled with numbers.

Suppose you are looking for a particular locality on the map. The index might tell you to look in square C3. Instead of searching through the entire map, you only have to search through one small square. This illustrates the use of a grid to make a large and complex map easy to use.

 

Guidelines for Sizing the Map Grid:

 

Predominant Plant Material

Suggested Grid Size

trees, some shrubs

200 ft. or 50 m.

shrubs, some herbaceous

100 ft. or 25 m.

small shrubs, herbaceous

50 ft. or 15 m.

conservatories and greenhouses

25 ft. or 10 m.

 

You must establish a numbering system for the grid. A combination of numbers and letters is most often used. In such a system, grid quadrants would have names such as F12 and G23 as described in the road map example above. Other numbering systems can also be used provided they are logical and consistent.


Placement of Markers

 

After a grid system is decided upon, markers must be placed in the ground to be used as reference points in determining plant locations. A professional surveying firm usually does the placement of the markers, although, with proper training and equipment, it could be done by your in - house staff.

It is not essential to place a marker at the grid line intersections. Markers can be placed at any convenient points from which you wish measure plant locations. If you will be using only a tape measure to determine plant locations, at least two markers must be placed within easy measuring distance of each plant to be mapped. If a total station electronic instrument will be used to determine plant locations, at least one marker must be placed within a line of sight of each plant to be mapped. Each marker must also be placed within sight of another marker. If you will be using the Global Positioning System (GPS), several markers should be placed as an aid in verifying the accuracy of GPS data.

Markers may be placed anywhere as long as their x and y coordinates are known and recorded, preferably on the markers themselves and on a map. If you will be using a transit or electronic instrument to determine the elevation of each plant, the elevation of each marker must be determined and recorded.

For the sake of economy, you may wish to place markers only at some key points that will be used for the initial mapping of your collection. Additional markers may be added later as time and budget permit. Or, you may decide to have some of the markers professionally placed and the remaining markers placed by in- house staff.

The markers should be of durable construction and should contain some metal so that they may be located with a metal detector should they become buried over time. A combination of metal and concrete is often used.

For more information on how to install markers, see Questions and Answers Involving Construction and Installation of Survey Markers.


Creating a Basemap

 

To set up a computerized mapping system, you will need a map of your property in CAD, GIS or other electronic format. This is called a basemap because it serves as a background onto which the plant information is drawn. The basemap must be coordinated with your grid system.

Information contained in the basemap can include grid lines, contour lines, buildings, roads, paths, and utilities. This information is usually grouped into a series of separate layers so that the type of information can easily be identified by color and so that some layers can be turned off (removed from the display) when not needed.

The creation of a basemap can vary greatly in complexity:

Starting From Scratch:

If you have no existing accurate maps of your property, you should hire a professional surveyor to create a map for you. This may be done by a combination of aerial and land surveying techniques. Make certain that the surveyor can deliver the map to you in GIS or CAD format so that it can easily be used with your computerized mapping system. Also, you will save time and effort if you provide the surveyor with your mapping system's standards for layering and text formatting. (If you are preparing for a BG-Map installation see BG-Map Layering Standards.)

Converting Existing Paper Maps or Aerial Photos:

If you have reasonably accurate conventional paper maps or aerial photos of your property, they can be digitized (converted into CAD or GIS form) by one of two techniques. The first technique requires that the paper maps or aerial photos be electronically scanned. Using AutoCAD or other software, the scanned images of the paper maps can be overlaid onto a CAD or GIS map. The information on the scanned map is then traced onto the computerized map.

The other technique involves taping the paper map or aerial photo onto an electronic digitizing table and tracing the information.

As the information is copied from the paper map into electronic form, it is grouped into appropriate layers. (If you are preparing for a BG-Map installation see BG-Map Layering Standards.) Information from a large number of paper maps can be combined to form a single composite electronic map.

It is important to keep in mind that the quality of the finished map will be limited by the accuracy of the original paper maps. If the original maps are not accurate, you may wish to consider discarding them and having the property resurveyed.

Using an Existing CAD or GIS Map:

If you are fortunate enough to already have a CAD or GIS map of your property, you should be able to adapt it for use with your mapping system with a minimum of modification.


Notes and Suggestions for Botanical Garden Surveyors
By Walt Dunlap Wayne Cahilly, Institutional Mapping Department, The New York Botanical Garden

Note: Walt Dunlap is no longer with the New York Botanical Garden. He may be contacted at wmdunlap@gmail.com

Part 1
|Setting Up Control Points| |Grid and Coordinate System| |Using a Total Station| |Elevations (Z Coordinates)| |Keeping a Field Notebook |
Part 2
|Palmtop Coordinates| |Temporary Points| |Checking Back In|
Part 3
|Total Station Care and Handling| |Total Station Pointing|
Part 4
|Using Radios to Communicate| |Courtesy|
Part 5
|The Difference between Accuracy and Precision| |Effects of Temperature and Pressure| |Leveling Vials - Meaning of Graduations|
Part 6
|Elevations and Vertical Offsets| |Datums|
Part 7
|Trigonometric Leveling|
Part 8
|Differential Leveling|
Part 9
|Locating Objects By Relative Measurement Or Baseline|
Part 10
|Magnetic Bearings|
Part 11
|A Simplified Glossary of Surveying Terms|
Part 12
|Using The STATIONS.FIL File|
Part 13
|Resection, or Finding the Coordinates of a New Control Point|
Part 14
|Using an Inverse Traverse Calculation to Locate a Lost Control Point|

   

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