Noxious Weed Infestation Mapping – One Suggested Strategy
I. Introduction
There are a variety of methods for conducting basic mapping of noxious woody or herbaceous weeds.
The following provides an overview of considerations for mapping, and a suggested strategy for
conducting basic on-the-ground noxious weed mapping if another method is not already being used
within your organization. It is important to note that while woody invasives such as tamarisk or Russian
olive may be the primary noxious weed targets for projects under this grant, it is equally as important to
assess project sites and plan treatment for important herbaceous noxious weeds that could prove
significantly problematic and inhibit restoration success. The following addresses the mapping of both
woody and herbaceous noxious weeds.
II. What to Know or Do Before Mapping A Site:
 Develop list of ‘Designated Weed Species of Concern’ for site and acceptable unique
abbreviations for each (e.g. RK for Russian knapweed). This list should be comprised of all
noxious weed species you would be willing to treat or might be concerned about. A useful
strategy is to combine the following two resources to create a comprehensive potential species
list for mapping, then refine this list as needed:
o Colorado Department of Agriculture Noxious Weed List:
https://www.colorado.gov/pacific/agconservation/noxious-weed-species
o Local County Noxious Weed List:
https://www.colorado.gov/pacific/agconservation/county-weed-programs
Your County Weed Manager (https://www.colorado.gov/pacific/agconservation/county-weedprograms) can help you refine the list for the species most likely to be present on your site.
 Know how to identify these ‘Designated Weed Species of Concern’ (and their look-alikes)
 Know the appropriate name of each site for map labelling, and make sure crew knows how to
get there
 Know approximate size and clear perimeter boundary of each site to be mapped (take a digital
or paper map of site with perimeter clearly marked to field)
 Determine what will be used for mapping the location of each weed infestation on your site (e.g.
basic handheld GPS unit, MapitFast©* software on a phone or tablet, Trimble©** unit, etc)
 Determine how you will be recording additional information associated with each mapped
infestation (see below). Will you be using a camera plus collecting this data on paper, or using a
digital format such as the ‘Notes’ section of MapitFast©, a digital form such as Strider©*
[MapitFast], or using a Data Dictionary such as with a Trimble©?)
 Determine if below mapping ‘rules’ work for your purpose (if not, revise as necessary). If so,
practice the following: (1) estimating area of infestation, (2) how to pace off a radius of 100 feet,
(3) how to estimate the average width of a ‘LINE’ infestation, and (4) estimating density/cover of
infestation. Make sure crew members understand difference between radius and diameter.
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III. Basic Mapping Data to Collect
Options for mapping the location of each weed infestation (with GPS or MapitFast Software, or similar)
are typically one of the following:
 Map infestation as a POINT
 Map infestation as a POLYGON
 Map infestation as a LINE
The minimum additional information associated with each mapped infestation to collect:
 Name of site
 Unique name of POINT, POLYGON, or LINE
 Name of weed species (this may be incorporated into the unique name of the POINT, POLYGON,
or LINE)
 GPS Accuracy at time of data collection (this may be recorded automatically) – This is important
to record for those revisiting the site, to know how accurate the recorded location is, or if they
will need to hunt around a bit
 GPS Datum being used (e.g. WGS 84) (check with mapping supervisor to make sure collecting
data in the right datum for your organization)
 Location of infestation (depends on device how this is recorded)
 Estimated Area of Infestation – If infestation is small, may just record as ‘One to a few plants’. If
larger, record actual estimated area. If infestation is quite large, may be easier to just estimate
radius for infestations mapped as a ‘POINT’, or width for infestations mapped as a ‘LINE’.
 Canopy cover/density of infestation (%)
 Fixed Photo Points: At a minimum, take a couple of pre-treatment photos of infestations that
will definitely be treated. Take photos from fixed points and record GPS coordinates (and datum
and accuracy) of each photo point so can easily return to exact same spot to take posttreatment photos.
 Other important notes relevant for treatment (e.g. is infestation near water body where water
safe herbicide and surfactant will be necessary, etc)
IV. In the Field – One Suggested Strategy for Noxious Weed Mapping
Systematically walk site to determine weed infestations on property. When a weed infestation is found
(infestation size can range from a single plant to a large infestation), walk around the area a bit to
determine if this is extent of infestation, or if extends further than originally thought. Try to get a sense
of the approximate infestation perimeter prior to actual mapping.
HOW TO MAP
The following example scenarios are for digital mapping in the field:
1) If infestation size ranges from a single plant to a small easily estimated infestation area:
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


Create a POINT for this infestation (go to approximate center of infestation to create
point)
Give point a unique name such as the following, especially if not using a digital Strider
form or Data Dictionary to collect this additional information. (Example = This is Site 1,
and you are mapping the first Russian knapweed (RK) infestation found (there may be
more). Name this point = “SITE1_RK1”
Collect additional information associated with each mapped infestation as determined
above. Record area of infestation as ‘One to several plants’, or estimate actual area of
infestation.
2) If infestation size is larger but does not cover entire site (and is not in the shape of a LINE such as
along a ditch or roadway): Walk to approximate center of infestation and estimate the radius
(not the diameter) of the infestation (imagine infestation contained within a circle):

If estimated radius of infestation is less than 100 feet:
 Create a POINT for this infestation (go to approximate center of infestation to
create point)
 Give POINT a unique name such as the following, especially if not using a digital
Strider form or Data Dictionary to collect this additional information. (Example =
This is Site 1, and you are mapping the first Russian knapweed (RK) infestation
found (there may be more). Name this point = “SITE1_RK1”
 Collect additional information associated with each mapped infestation as
determined above. Record area of infestation as ‘Radius = 30 feet’ (for
example); then in office can calculate total area of infestation ‘circle’ [Area = π
r2] (and map using buffering tool if you want)

If estimated radius of infestation is equal to or greater than 100 feet:
 Create a POLYGON for this infestation by walking slowly around perimeter of
infestation (if walk too fast, your ‘corners’ will get cut off because GPS won’t be
able to keep up with you). If it is a very large population, have partner walk
ahead of you and find perimeter for you so that you can just follow partner
(otherwise your perimeter line will zig zag all over the place).
 Give POLYGON a unique name as described above
 Collect additional information associated with each mapped location.
Note: Your device may automatically record the area of infestation when
mapping the polygon, so you may not need to determine/record the
area of infestation separately (but double-check this).
3) If infestation size is larger but does not cover entire site (and IS in the shape of a LINE):


Create a LINE for this infestation by walking infestation from one end of the other
Give LINE a unique name as above
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
Collect additional information associated with each mapped infestation as determined
above. For recording area, estimate average width of infestation, then record area of
infestation as ‘Width = 10 feet’ (for example); then in office can calculate total area of
infestation ‘rectangle’ [Area = l x w] (and map using buffering tool if you want)
4) If infestation is generally spread across entire site:

If site is large and don’t want to walk entire perimeter of infestation, your mapping device
may allow you to simply draw in the infestation, or if not, one option is to temporarily map
infestation as a POINT, and record area of infestation as ‘Spread Across Entire Site’; then in
office use this temporary POINT information to create a POLYGON the size of the entire site
and transfer the data over.
*The MapitFast© mapping application - and associated Strider©software - are mentioned in this
document only to provide an example of simple mapping software available for those conducting basic
weed mapping who may not have access to or sufficient knowledge of ArcGIS software.
**The Trimble© unit is mentioned in this document only to provide an example of a GPS unit that may
be more advanced and accurate than the basic hand held GPS unit.
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Sample Site Weed Mapping (Map, Basic Data, Photo Points)
Site 1
Weed Species
Estimated Area of
Infestation
Estimated Density of
Infestation (%)
Photo Point
Taken?
Russian knapweed 1 (Acroptilon
repens)
1-5 plants
100%
No
Russian knapweed 2
20 square feet
50%
No
Whitetop (Cardaria draba)
400 square feet
50%
Photo Point 1
Tamarisk (Tamarix sp.)
1.5 acres
75%
Photo Point 2
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Photo Points
Photo Point 1 – Whitetop infestation
Pre-Treatment – July 15, 2015
Post-Treatment
0666700 E, 4291001 N; Datum = UTM NAD 83; Accuracy: 12
feet
Photo Point 2 – Tamarisk infestation
Pre-Treatment – Dec 5, 2015
Post-Treatment
0666700 E, 4290775 N; Datum = UTM NAD 83; Accuracy: 16 feet
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