SAMPLE POINT GENERATOR
An ArcView 3.2+ Application
Acknowledgements
Forest Health Technology Enterprise Team would like to acknowledge both the San Dimas Technology and
Development Center and Colorado State University and for their support in this effort. We would also like to thank the
Inventory and Monitoring Technology Development (IMTD) Steering Committee for partial funding of this User’s Guide.
Sample Point Generator (SPGen): Users Manual
SAMPLE POINT GENERATOR
An ArcView 3.2+ Application
Authors
Vern Thomas, FHTET
Marla Downing, FHTET
Robin Reich, Colorado State University
Sample Point Generator (SPGen): Users Manual
SAMPLE POINT GENERATOR
An ArcView 3.2+ Application
The Sample Points Generator (SPGen) ArcView
application allows the user to quickly create sample points
within any area of interest for data or field sampling.
There are five basic categories from which to create
sample points.
 SAMPLE POINTS WITHIN THEME EXTENT
 SAMPLE POINTS WITHIN SELECTED POLY(S)
 EQUAL NUMBER SAMPLE POINTS IN POLY’S
 AREA WEIGHTED PROBABILITY SAMPLE
POINTS
 SYSTEMATIC SAMPLE POINTS
Four of the five categories have two sampling routines:
1) Basic and 2) Minimum Distance (Systematic Sample
Points () does not have minimum distance).
CLASSIC – Sample points created are truly
random with no minimum distance
constraint.
Random Point
Generator Options





MINIMUM DISTANCE – Theses functions
have a user-entered minimum distance
between sample points. The greater
the distance, the more regular/systematic
the sample point pattern becomes.
This is useful when the user needs
a more even sampling across the area
of interest.
Sample Point Generator (SPGen): Users Manual
Page 1
SAMPLE Point Generator
1A  Random Points Within
Theme Extent: CLASSIC

Definition
Random points are generated across the
theme extent where the points fall within
polygon features. Themes with many
polygons may have some of those
polygons with no sample points and
others that contain many.
This option is useful when the user has a
theme containing two or more polygons and
wants to create true random points throughout
the theme area regardless of how many points
may or may not fall within each polygon.

 Random points are generated within the
theme’s overall extent only where they fall
within any theme polygon feature. From the
MALE SAMPLE POINTS pull-down, select
1A Random Sample Points: BASIC.
 The Select POLYGON Theme popup
window appears. Select the polygon theme
in which you want to create sample
points and single-click the OK button.
 Next, select the sample point theme from
Select Sample Point Theme popup window
and single-click the OK button.
continue 
Sample Point Generator (SPGen): Users Manual
NOTE: You can use
this function with
single polygon
themes (e.g., forest
boundary).

Page 2
SAMPLE Point Generator
1A  Random Points Within
Theme Extent: CLASSIC

continued from page 2
 The Enter The Number of Sample Points
To Create popup window appears. Enter the
desired number of sample points and singleclick the OK button. At this point, the system
will begin creating the random sample points.
 Typical results of using the Random
Sample Points in Theme Extent: BASIC
function. Notice that the distribution of
sample points includes some large open areas
with no points, and other areas where the
points are more clustered: this is typical
of a random point pattern.
Sample Point Generator (SPGen): Users Manual

Page 3
SAMPLE Point Generator
1B  Random Points Within
Theme Extent: MIN DISTANCE

Definition
Random points are generated within
theme extent and and as long as the
points intersect any polygon feature within
the theme. Points are located no closer
than the user-entered minimum distance
between sample points.
This option is useful when the user has a
theme containing two or more polygons and
wants to create random points that have a
minimum distance from each other throughout
the theme area regardless of how many points
may or may not fall within each polygon.
 From the MAKE SAMPLE POINTS
pull-down menu, select the 1B Random
Sample Points: MIN DISTANCE option.
 The Select POLYGON Theme popup
window appears. Select the polygon theme
to receive sample points and single-click the
OK button.

continue 
Sample Point Generator (SPGen): Users Manual
Page 4
SAMPLE Point Generator
1B  Random Points Within
Theme Extent: MIN DISTANCE
Continued from page 4
 The Select Sample Point Theme popup
window appears. Select the sample point
theme and single-click the OK button.
 The Enter Minimum Distance popup
window appears. Enter a minimum distance
between sample points and singleclick the OK button. In this example, the
minimum distance is set at 1609 meters
(1 mile). Notice that the system estimates and
suggests the greatest value that the minimum
distance should be set. In this example, any
value less than 2749 meters should work
without loosing sample points due to too
many sample point for a particular area based
on the minimum distance entered.


The Enter The Number of Sample Points
To Create popup window appears. Enter the
desired number of sample points and singleclick the OK button.
NOTE: It is important to know your data’s
projection so you will know the correct units
to enter for minimum distance. (continue )
Sample Point Generator (SPGen): Users Manual
Page 5
SAMPLE Point Generator
1B  Random Points Within
Theme Extent: MIN DISTANCE

Continued from page 5
 At the Enter the Number of Sample
Points to Create input window, enter the
desired number of sample points to create.
Notice that the input window indicates a
maximum number of sample points to enter.
In this example, the system estimates that the
maximum number of sample points is 218.
This number is based on the entered minimum
distance enter in the previous step and should
be used as a guide only. In our example, we
entered 100 sample points (well under the
estimates maximum).

 Typical results of using the 1B  Random
Sample Points: MIN DISTANCE function.
Notice that the pattern of the sample points
includes some large open areas with no points,
but no areas of closely clustered points due to
the limits of the minimum distance between
points (compare these results to the CLASSIC
model results).
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
2A  Points Within Selected
Polygon(s): CLASSIC
Definition
True random points are generated within
a selected polygon or set of polygons
within a theme.

This option is useful when the user has a
theme containing two or more polygons of
interest and wants to create true random points
within specific polygonal areas (e.g., stands)
for a field crew to visit or statistical sampling.
 The user selects the polygon or polygons to
receive random sample points. Use the
ArcView Feature Selection tool to select the
polygon(s).
 From the Random Points pull-down menu,
select the 2A  Random Sample Points:
CLASSIC option.

continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
2A  Points Within Selected
Polygon(s): CLASSIC
continued from page 7
 The Select Polygon Theme popup
window appears. Select the theme containing
the selected polygon(s) to receive random
sample points. Single-click the OK
button to continue.

 Next, from the Select Sample Point
Theme popup window, select the sample
point theme and single-click the OK button
to continue.
 Enter the total number of sample points to
be placed within the selected polygons and
single-click the OK button. In this example,
the user entered 20 sample points. The
system then begins to create the random
sample points. See the next page for the
results of the random point generation ().


continue 
Sample Point Generator (SPGen): Users Manual
Page 8
SAMPLE Point Generator
2A  Points Within Selected
Polygon(s): CLASSIC
continued from page 8
 The results of the random sample points
within the selected polygons. Notice that the
sample points fall only within the selected
polygon feature(s) of the theme. Also notice
that the pattern of the sample points includes
some large open areas with no points, and
other areas where the points are more
clustered. This is typical of a random point
pattern.
Sample Point Generator (SPGen): Users Manual

Page 9
SAMPLE Point Generator
2B  Points Within Selected
Polygon(s): MIN DISTANCE
Definition
Random points are generated within
selected polygon(s) only and points are
located no closer than the user entered
minimum distance between sample
points.

This option is useful when the user has a
theme containing multiple polygons and wants
to create evenly distributed sample points
within a polygon area for a field crew to visit.
 User selects the polygon or polygons to
place random sample points within. Use the
ArcView Feature Selection tool to select the
polygon(s)
 From the Random Points pull-down menu,
select the 2B  Random Sample Points:
MIN DISTANCE option.

continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
2B  Points Within Selected
Polygon(s): MIN DISTANCE
continued from page 10

 From the Select Polygon Theme popup
window, select the theme containing the
selected polygon(s). Single-click the OK
button to continue.
 Next, from the Select Sample Point
Theme popup window, select the sample
point theme, and single-click the OK button to
continue.
 Enter the minimum distance between
sample points. In this example, the user
entered 1000 meters and single-click the
OK button.
NOTE: SPGen gives the user some
guidance in regard to an appropriate
minimum distance. In the example, SPGen
calculated an estimated minimum distance
less than 1423 meters given the area of the
selected polygons. Use this as a guide, not an
absolute value. It is best to experiment with
different minimum distances.

Estimated Minimum Distance

continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
2B  Points Within Selected
Polygon(s): MIN DISTANCE

continued from page 11
 Enter the number of sample points to
create within the selected polygons.
NOTE: SPGen calculates the maximum
Number of sample points that can be created
given the area of the selected polygons and
the minimum distance entered in the
previous step. In the example to the right,
SPGen has estimated that the user may enter
a maximum of 28 sample points. In this case
we entered 20 sample points. Single click
the OK button to continue.

NOTE: It is important to know your data’s
projection so you will know the correct units
to enter for minimum distance.
 The results of the random sample points
within the selected polygons. Notice that the
sample points fall only within the polygon
feature(s) of the theme. Also notice that the
pattern of the sample points is more evenly
distributed with no areas of closely clustered
points due to the limits of the minimum
distance between points.
Sample Point Generator (SPGen): Users Manual
Page 12
SAMPLE Point Generator
3A  Equal Number Random
Points in Polygons: CLASSIC
Definition
The system creates a user-defined
number of random points generated within
each polygon of a theme (e.g., 6 points
per polygon).

This option is useful when, for instance, the
user has a stand polygon theme containing
multiple polygons and needs to have the same
number of sample points in each stand
regardless of stand area.
 From the Random Points pull-down menu,
select the 3A  Random Sample Points:
BASIC option.

 From the Select POLYGON Theme popup
window, select the polygon theme to receive
random sample points. Single-click the OK
button to continue.
 From the Select Sample Point
Theme popup window, select the sample
point theme and single-click the OK button.
Something in
continue 
Sample Point Generator (SPGen): Users Manual
NOTE: This function will create
sample points in every polygon
in the theme unless there is a
selected set of polygons. If there
is, it will create sample points
only in the selected polygons.

Page 13
SAMPLE Point Generator
3A  Equal Number Random
Points in Polygons: CLASSIC

continued from page 13
In the Enter the Number of Sample
Points popup window, enter the number of
points to be placed in the largest polygon
area. In this example, the user entered “5” as
the number of random points to be placed in
each of the theme’s polygons.
 Typical random sample points results
using the 3A  Equal Number Random
Points in Polygons: CLASSIC function.

NOTE: The points will look clustered in
smaller polygons and generally more widely
spaced in larger polygons.
Sample Point Generator (SPGen): Users Manual
Page 14
SAMPLE Point Generator
3B  Equal Number of Random
Points in Polygons: MINIMUM
DISTANCE
Definition
The system creates a user-defined
number of random points generated within
each polygon of a theme (e.g., 6 points
per polygon). Random points are
generated within each polygon and are
located no closer than the user-entered
minimum distance.
This option is useful when, for instance, the
user has a stand polygon theme containing
multiple polygons and needs to have the same
number of sample points in each stand with a
minimum distance between points.
NOTE: Smaller polygons may not get the
full complement of sample points!!!


 From the Random Points pull-down menu,
select the 3B  Random Sample Points:
Minimum Distance option.
 From the Select Polygon Theme pop-up
window, select the polygon theme to receive
sample points.

 From the Select Sample Point Theme
pop-up window, select the sample point theme.
continue 
Sample Point Generator (SPGen): Users Manual
Page 15
SAMPLE Point Generator
3B  Equal Number of Random
Points in Polygons: MINIMUM
DISTANCE
continued from page 15
NOTE:
It is important to
know your data’s
projection so you
will know the correct
units to enter for
minimum distance.


 Enter the number of random points to be
placed in each polygon and click OK. In this
case, we want 5 sample points per polygon
regardless of polygon area.

 Enter the minimum distance between
sample points in meters. In this example, the
user entered 800 meters (~1/2 mile). Notice
that SPGen estimates the the largest minimum
distance based on the smallest polygon in the
theme. In this case, however, the user desires
800 meter minimum distance.
 A report box may appear if some polygons
did not receive the allotted number of points.
This may occur if a polygon has too small an
area to accommodate the number of sample
points with the minimum distance. You can
choose to keep the points or reduce the
minimum distance or reduce the number
of points (or both) and rerun.

 Typical results of 3B  Equal Number of
Random Points in Polys: MIN DISTANCE.
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
4A  Area Weighted Probability
Random Points: CLASSIC
Definition
The user first enters a total number of
random points to be created and the
points are then distributed within the
polygons where the larger the polygon
area, the more probability that that a
random sample point will be placed
within the polygon.

Example:
You would use this design when the variable
of interest is correlated to size of the polygon
such as forest surveys where the larger stands
will contribute more to the overall mean than
the smaller stands. If the variable of interest is
Not correlated to to polygon size, then the
variance may be larger than if you did a
simple random sample.
 From the Random Points pull-down menu,
select the 4A  Random Sample Points:
CLASSIC option.
 From the Select Polygon Theme popup
window, select the theme containing the
selected polygon(s) to receive random sample
points. Single-click the OK button to continue.

NOTE!!!
The system will quickly
calculate area and probability
ranges. This make take a few
seconds to a few minutes
depending on the size of the
theme.
continue 
Sample Point Generator (SPGen): Users Manual
Page 17
SAMPLE Point Generator
4A  Area Weighted Probability
Sample Points: CLASSIC

continued from page 17
NOTE: The system calculates area ranges
and probabilities before continuing onto step 3.

 From the Select Sample Point
Theme popup window, select the sample
point theme and single-click the OK button.
 Enter the total number of sample points
to create within the theme and single-click
the OK button. The system will then begin
to create sample points.
 Results of the Area Weighted Probability
random sample point process. Notice that the
pattern of the sample points is random and
that some of the smaller polygons contain no
sample points while the larger polygons
contain more points.
Sample Point Generator (SPGen): Users Manual

Page 18
SAMPLE Point Generator
4B  Area Weighted Probability:
MINIMUM DISTANCE
Definition
Random points are generated within the
theme polygons. The probability that a
polygon will receive a random sample
point increases with the size (area) of
the polygon. The user enters a total
number of points to create and the points
are then distributed within the polygons
where the larger the polygon, the more
probability that that polygon will have a
random sample point placed within itself.
Random points are generated within each
polygon and are located no closer than
the user entered minimum distance
between sample points.

This is useful when the user is doing a spatial
statistical analysis of the landscape. The user
may need a specified number of random
sample points with a more regular pattern and
which have a representative distribution by
area from the different cover type polygons.
 From the Random Points pull-down menu,
select the 4B  Random Sample Points:
MIN DIST option.
continue 
Sample Point Generator (SPGen): Users Manual
Page 19
SAMPLE Point Generator
4B  Area Weighted Probability:
MINIMUM DISTANCE
continued from page 19

 From the Select Polygon Theme popup
window, select the theme containing the
selected polygon(s) to receive random
points. Single-click the OK button to
continue.
 From the Select Sample Point
Theme popup window, select the sample
point theme and single-click the OK button.

 Enter the total number of sample points
to create within the theme and single-click
the OK button.
 Enter the minimum distance between
sample points in meters. In this example,
the user entered 1609 meters (1 mile).
SPGen will then begin to create sample
points. Notice the system estimates the
largest minimum distance to use given the
area of the theme. In this example, it
suggests that the user may use a minimum
distance of 2749 meters or less.


continue 
Sample Point Generator (SPGen): Users Manual
Page 20
SAMPLE Point Generator
4B  Area Weighted Probability:
MINIMUM DISTANCE
continued from page 20
 Typical results of the Area Weighted
Probability: Min Distance random point
function. Notice that the pattern of the
sample points appears fairly regular, though
it does include some open areas with no
points, but no areas of closely clustered points
due to the limits of the minimum distance
between points

NOTE: If the minimum distance is too great
given the number of sample points entered,
SPGen will attempt to create as many
sample points as possible. When it cannot
solve for anymore points it will pop-up
a warning message informing the user that
it cannot populate all requested sample points
and that the user should either reduce the
minimum distance or the number of sample
points.
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
5  Make Systematic Grid Cell
Polygons
Definition
A polygon can be populated with sample
points within a system of grid cells to
support homogenous sampling across the
polygon. Placement of points within the
cells can be random or aligned. Before
these points can be assigned, however,
the user must select the polygon and
define the grid pattern for it.

Use this design when there is a gradient in the
population being sampled. If the variable of
interest is randomly distributed, there will be
no difference between this method and a
simple random sample. Systematic sampling
may also cost less by minimizing travel time.
 Select the polygon(s) that you want to
place systematic sample points within.

You do not have to select any polygons if you
want the entire theme to be covered by the
systematic grid.
 From the Random Points pull-down
menu, section, select the 5  Make
Systematic Cell Polygons option.
continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
5  Make Systematic Grid Cell
Polygons

continued from page 22
 From the Select Systematic Cell Theme
popup window, select the systematic cell
theme (this shape file comes as part of your
ZIP file). If you don’t have this file in the
view, then load it before continuing. Singleclick the OK button to continue.
 Select the theme in which you want to
create the systematic grid cell polygons and
create random sample points.

 Enter the cell size for the systematic grid
in meters. In this example, the user entered
1609 meters (1 mile). In other words, there
will be a single random point located within
each 1 mile by 1 mile square area (refer to
page 26).

continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
5  Make Systematic Grid Cell
Polygons
continued from page 23
 The results of creating the systematic grid
cell polygons.
Notice that the system creates systematic cells
around any combination of selected polygons
or, if no polygons are selected, SPGen will
create systematic cells over the entire theme
extent.
Sample Point Generator (SPGen): Users Manual

Page 24
SAMPLE Point Generator
5A  Non-Aligned Systematic
Points: Random Within Cell
Definition
Sample points are placed randomly within
each theme grid cell to give
comprehensive coverage and maintain a
random structure to the sample points.
This option is useful when a the user wants to
sample “evenly” across an area (polygon)
while still maintaining randomness required
for statistical analysis.
 From the Random Points pull-down menu,
select the 5A  Non-Aligned in Systematic
Points: Random Within Cell option.


 From the Select Systematic Cell Theme
popup window, select the systematic theme
shape file and single-click the OK button.
 From the Select Sample Point Theme
popup window, select the sample point
theme and single-click the OK button.
The system will then begin to create a
random sample point within each grid cell
polygon. Refer to the next page typical results
for this random sample routine.

continue 
Sample Point Generator (SPGen): Users Manual
Page 25
SAMPLE Point Generator
5A  Non-Aligned Systematic
Points: Random Within Cell
continued from page 25
 Results of the non-aligned systematic
random points within cell function.

Sample Point Generator (SPGen): Users Manual
Page 26
SAMPLE Point Generator
5B  Aligned Systematic Points:
Centered Within Cell
Definition
A single random point is placed within
the center of each grid cell, creating a
complete regular pattern distribution of
sample points. The dimension of the grid
cell is the distance between points.
This option is useful when when a regular
sampling process is required and terrain
allows.
 From the Random Point pull-down menu,
and select the 5B  Aligned Systematic
Points: Centered Within Cell option.


 From the Select Systematic Cell Theme
popup window, select the systematic theme
shape file and single-click the OK button.
 From the Select Sample Point Theme
popup window, select the sample point
theme and single-click the OK button.
The system will then begin to create a
random sample point within each grid cell
polygon. See the next page for typical results
of this random sample routine.

continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
5B  Aligned Systematic Points
continued from page 27
 The results of the aligned systematic
random points function. This option creates
a completely regular pattern using the center
of the cell as the point location.
Sample Point Generator (SPGen): Users Manual

Page 28
SAMPLE Point Generator
6A  Random Sampling from
Existing Sample Points
Definition
This function allows the user to randomly
select a user-entered number of points
from an existing sample point theme.
Use this when to resample a population in
order to make inference about changes that
have taken place in the population over a
given time period.

 From the Random Points pull-down menu,
select the 6A  Select Random Points
From The Sample Point Theme option.
 Select the sample point theme that contains
the input sample points you want to select
from and single-click the OK button.
 The user enters the number of points
to select from the existing sample point theme.
In this example, the user entered 100 random
points to select from the sample point theme,
which contains 411sample points. Single-click
the OK button. The system then randomly
selects the desired number of points. The user
can create a new point file from the selected
polygons, or delete some of the selected points.
continue 
Sample Point Generator (SPGen): Users Manual


Page 29
SAMPLE Point Generator
6A  Random Sample from
Existing Sample Points
Continued from page 29
 Results of the random selection of points
from the existing sample points theme. In this
view, dark points represent the original, nonselected points in the points theme, and light
points represent selected sample points.
Sample Point Generator (SPGen): Users Manual

Page 30
SAMPLE Point Generator

Creating an ASCII file of Random
Point Coordinates
Definition
Coordinates for sample points can be
used in a GPS with the ability to upload
coordinates in an ASCII format. The
following instructions describe the process
of exporting the sample point theme’s
table to a comma-delimited text file
(ASCII).

Note: This is an ArcView function not tied to
the random points generation routine. Details
are available in ArcView documentation.
 Set the Sample Points theme as the active
theme within the View's theme table of
Contents.
 Click on the Open Table of Active Theme
Button to open the table of the Sample Points
Theme.

 The Sample Point Table appears.
continue 
Sample Point Generator (SPGen): Users Manual
Page 31
SAMPLE Point Generator
Creating an ASCII file of Random
Point Coordinates
continued from page 31

 From the File menu pull-down, select the
Export function.
 The Export Table popup window
appears. Select the Delimited Text option
and single-click the OK button to continue.

 The Export Table browse and file name
popup window appears. Browse to the
proper directory to store the new text file
and name the file. Click the OK to complete
the process. The new text file has now been
written.

continue 
Sample Point Generator (SPGen): Users Manual
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SAMPLE Point Generator
Creating an ASCII file of Random
Point Coordinates
continued from page 32

 Example of the exported sample points
text file as viewed in MS Notepad. This file
can be modified by deleting any unwanted
information except the point ID number,
X coordinate, and Y coordinate; then it is
ready for upload into a GPS.

 Another method is to load the comma
delimited text file into MS EXCEL, delete
the extraneous columns, and save again as
a text file (as seen in example )

Sample Point Generator (SPGen): Users Manual
Page 33