Proximity Analysis

1
Proximity Analysis

• Jessie Powers

2
What is proximity analysis?

• Proximity analysis is one way of analyzing
  locations of features by measuring the distance
  between them and other features or cells.
• The distance between point A and point B may be
  measured 2 ways
• As a straight line
• By following a networked path, such as a street
  network or river system

3
How does it work?

• The Proximity toolset contains tools that
  determine the proximity of features within a
  coverage or between two coverages. These tools
  can identify features that are closest to one
  another and calculate the distances around and
  between them.
• The Proximity tools can create entire new
  shapefiles from your calculations, or just add
  attributes to already existing coverages
• Popular uses
• - zoning
• - watershed studies
• - demographics

4
Tools of the Trade

• Buffer - Creates a new coverage of buffers around
  specified features (points, lines, polygons, or
  nodes) in a coverage.

5

• Near - Computes the distance from every point in
  input feature to the nearest input feature point,
  line, or node. Results are recorded in the output
  coverage point attribute table.

6

• Point Distance - Computes distance from each
  point in a feature to all points in the same
  coverage or a different coverage within a
  specified radius.

7

• Point Node - Transfers attributes from a point
  feature class to a node feature class

8

• Select by Location - Selects features from a
  target feature class within a given distance of
  (or using other spatial relationships) the input
  features.
• Creates, updates, or removes a selection on the
  input layer based on spatial relationships to
  select features.
• Tip The input must be a feature layer or a
  table view. It cannot be a feature class or
  table.

9

• Thiessen Polygons - Converts a point coverage to
  a coverage of Thiessen or proximal polygons. Each
  polygon contains only one input point, and any
  location within a polygon is closer to its
  associated point than to the point of any other
  polygon.

10
Where do I find these tools?

• All of the proximity analysis tools are found in
  ArcToolbox

Actually, we only get Buffer, Near and Point
Distance. awwww
11
Time for an example

• As an avid hiker and adventurer, I was more than
  happy to lend my GIS expertise to Morven Farm
  when they were thinking of doing some trail
  renovation
• State mandate calls for all trails to be at least
  20ft from waters edge for safety purposes, and
  the owners believe several spots on the trail may
  be in danger
• Time to get started!

12
So I want to create a 20ft boundary around each
of the ponds (light blue) so I will know how
close the hiking trails (dark red) can come and
still be safe
13
Its Simple!

• Go to the Buffer Tool and fill in the
  appropriate fields

14

• I have morven_pond as my input and I make sure I
  save my output to the folder with all my other
  data
• In this case, I want to use the linear unit
  instead of the field because I know exactly the
  distance I want, and I leave the side type as
  full and the end type as round
• TIP I also find it easier to change the
  color of your output shapefile to hollow so you
  can actually see it in relation to your original
  shapefile (in this case, the ponds)

15
Hit OK and youre done! Just from this
zoomed-in view, I can see my trails are in danger
in a couple locations. Oh no!
16
What you get

• With the execution of the Buffer tool, you
  create an entirely new shapefile.

17
Moving On

• The nice people at Morven Farm were so impressed
  with my work, they gave me a new project
• I have to determine the distance from each of the
  buildings on Morven Farm to the main trail on the
  property
• With over 74 buildings, this is going to take
  forever!

18
Never fear, I can use Near

• The Near tool will allow me to find the
  distance from each building (red point) to the
  closest section of the trail

19
I use morven_buildings as my input (because its
the only point layer I have!) and the
morven_trails as my near feature. I leave the
radius empty because I dont know the distances
20
It doesnt look any different
But wait! All my distances are in the attribute
table for my morven_buildings coverage
21
Being the over-achiever that I am, I even decided
to determine what angle the trail is relative to
the buildings so people would know which
direction to walk.

• Its simple just click the angle box on the
  Near tool and youve got it

22
What you get

• With the execution of the Near tool you get a
  new column in the attribute table of your already
  existing point coverage
• You have the option to get distance, angle, X,Y
  coordinates, or all three

23
Not done yet

• Summers here in VA can get kind of dry, so the
  nice people at Morven far were considering
  installing sprinklers at each of the 74 buildings
• They want to know what gauge sprinkler theyll
  have to install based on the area surrounding
  each building
• So how can I determine the area each sprinkler
  should have to cover to be efficient (the
  sprinkler can cover the allotted area, but wont
  overlap with nearby sprinklers)?

24
Use Thiessen Polygons!
25
For input features, I have to use my only point
layer morven_buildings. Since I want to retain
any attribute data associated with the buildings,
I choose ALL as my output field
26
The result is a new shapefile of 74 individual
polygons (one generated for each point) in which
the contained point is closer to any location
within its polygon boundaries than to another
point. This shows the area each sprinkler would
be responsible for covering.
27
Just like Near

• Point Distance is very similar to the near tool
  except that it uses only point coverages
  (distances between just points).

28
This is a job for Point-Distance

• The distances between the Lawrence, SD
  climatology lab (red star) and the mountain-top
  weather stations (green dots) would show up as a
  table
• TIP When using the Point-Distance tool, the
  smaller radius the better because the output
  table becomes very large very quick

29
Everybodys using it

• While these may be trivial examples, proximity
  analysis tools are very useful in a variety of
  settings
• Buffer
• could be used to determine safe distances for
  animal runoff between cow pastures and rivers
  feeding reservoirs
• How close a new housing development could be
  built to the interstate without excessive road
  noise

30

• Near
• could show how many grocery stores are located
  within a 1 mile radius (walking distance) of the
  city bus route
• How far the closest 7Eleven is off Rt. 29, and
  what direction youll have to go
• How close nesting sites of endangered turtles are
  to major highways

31

• Point Distance
• Compare distances between businesses (such as
  theaters, fast food restaurants) and locations of
  community problems (litter, broken windows,
  spray-paint graffiti), limiting the search to one
  mile to look for local relationships.
• Find which public parking lot is closer to your
  favorite music venue/bar on the Downtown Mall

32

• Thiessen Polygons due to the development of
  more advanced proximity tools (such as the ones
  weve looked at today), thiessen polygons are
  used less frequently in environmental and
  planning jobs today.
• Could be used to determine the area serviced by
  each grocery store within a county
• However, with a little investigating, I found 2
  cases in which Thiessen Polygons were the only
  way to go
• 1860 Census Officers Route in Shenandoah Valley
• Guessing the boundaries of Chinese cities and
  military facilities with only a given point

33
Some Tips

• Buffer and Thiessen Polygons are the easy
  ones - they create new shapefiles you get to see
  right away.
• Near and Point Distance are a little trickier
  and only create a new attribute for your existing
  shapefile.
• Remember
• Buffer can use points, lines or polygons
• Near and Thiessen Polygons require at least 1
  point layer
• Point Distance requires at least 2 point layers

34
Questions?

• References and Image Sources
• http//support.esri.com/ (its great!)
• Scholars Lab (theyre real nice too!)