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Spatial Analysis - cont. There are four traditional types of spatial analysis: Topological overlay and contiguity analysis Surface analysis Linear analysis Raster analysis Add new hyperlinks for the yellow words Read more abt contiguity and other analyses
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Definition of Spatial Analysis
Spatial analysis - The process of modeling, examining, and
interpreting model results. Spatial analysis is useful for
evaluating suitability and capability estimating and predicting
interpreting and understanding Add new hyperlinks for the yellow
words Spatial Analysis - cont.
There are four traditional types of spatial analysis: Topological
overlay and contiguity analysis Surface analysis Linear analysis
Raster analysis Add new hyperlinks for the yellow words Read more
abt contiguity and other analyses Definition of Spatial
Analysis
Spatial data analysis involves the application of operations to
coordinate and relate attribute data. Spatial Analysis -
cont.
Spatial analyses are applied to solve problems related to
geographic decisions Identify high crime area Generate a list of
roads that contribute towards NPS pollution Selection of a best
location for a new business Determine the spread of nucleotides in
underground aquifer Extent of sage brush infestation in Idaho.
Spread of a disease in western states of US. Definition of Spatial
Analysis - cont.
Spatial analysis deals with function and operation interchangeably.
Spatial operations could be applied sequentially An output could
serve as input Sequence of spatial operations is important Bolstad,
2005 Definition of Spatial Analysis - cont.
Bolstad, 2005 one input can have many outputs many inputs can have
one output Spatial Operations Local operations Neighborhood
operations
Global operations Use only data at one input location to determine
value at corresponding output location : Use data from both an
input location and nearby location to have output value : Use data
value from entire input layer to have each output value Bolstad,
2005 Spatial Operations - cont.
Spatial operation types Selection Classification Selection
Selection operations Examples
Involve identifying features based on several conditions or
criteria The attributes or geometry of features are checked against
the conditions or criteria You can write the selected features into
new output data layer You can use the selection for other analysis
Examples Select: State = Arkansas States = entirely north of
Arkansas
States_area>84,000 sq. mi. States both entirely north of
Arkansas and larger than 84,000 sq. mi. Bolstad, 2005 Functions of
Spatial Analysis
Conditional selection Set Algebra Less than () Equal to (=) Not
equal to () Boolean Algebra Conditions OR, AND, and NOT Bolstad,
2005 Examples of Expression in Boolean Algebra
Bolstad, 2005 Select by Location - cont.
Selecting options That Meet That Overlap That Contains That are
Contained by That are Entirely Contained By That are Spatially
Equal That Touch Click on the white text box to show a list of
themes and select the theme that contains the layer you want to
query. You can change this later if the layer is not in the theme
you select. For the example select Gazetteer Click on the white
text box to show a list of layers within the theme and select the
layer you want to query.For the example select Addresses If you
want to display all records of your chosen layer within your chosen
boundary accept the default, Display all layer records and if you
want to filter the records of your chosen layer within your chosen
boundary then click next to Query layer records This defines how
the records you are looking for, the first record set, should
interact with the second record set That Meet: Includes only
features referenced by the first record set that meet features
referenced in the second record set. That Overlap: Includes only
features referenced by the first record set that overlap features
referenced in the second record set. That Contains: Includes only
features referenced by the first record set contain features
referenced in the second record set. That are Contained by:
Includes only features referenced by the first record set that are
contained in the second record set. That Entirely Contains:
Includes only features referenced by the first record set that
completely contain the features referenced in the second record
set. The boundaries of the features cannot touch in any way;
everything must be interior. That are Entirely Contained By:
Includes only features referenced by the first record set that are
completely contained in the second record set. The boundaries of
the features cannot touch in any way; everything must be interior.
That are Spatially Equal: Includes only features referenced by the
first record set that are spatially equal to features referenced in
the second record set. That Touch: Includes only features
referenced by the first record set that intersect features
referenced in the second record set. Examples of Selection by
Location
States adjacent to Missouri Bolstad, 2005 Examples of Selection by
Location - cont.
States containing a portion of Mississippi River or its tributaries
are selected Bolstad, 2005 Classification Categorization of
geographic objects based on a set of conditions Also known as
reclassification or recoding Spatial data operation can be used
along with selection operation Example: classify polygons based on
size Bolstad, 2005 Classification - cont. Classification is an
operation to create a new group of classes froman existing set of
classes Classification is governed by a a table or array (decided
by user before hand) Bolstad, 2005 Classification - example
Classification of land use for obtaining your required information
Classification - cont. Manual classification Binary
classification
Example (Last slide) Binary classification You need to have two
classes 0 and 1 True or false A and B Some other two level
classifications Bolstad, 2005 Automatic Classification
Good for many classes in one feature file (when it is practically
not possible to manually classify into groups) Requires
classification schemes (algorithms or mathematical formula) which
will combine various classes into a single group Equal interval
Defined interval Quantile Natural breaks (Jenks) Standard deviation
Classification Examples
Quantile classification Bolstad, 2005 Spatial Analysis
Functions
Buffer Clip or window Overlay Intersect Union Identity Near or
Distance (proximity) Dissolve These spatial analysis techniques in
Arc/Info are: 1.Buffer 2. Clip 3. Intersect 4. Union 5. Identity 6.
Near 7. Dissolve The spatial analysis techniques in Idrisi are:
2.Window (clip) 3.Overlay (intersect, union) 4.Distance(near)
Buffer one of the most common spatial analysis tools
specific distance representation around a feature The distances can
either be constant or can vary depending upon attribute values.
When features are close together, their buffers may overlap.The
user can choose to preserve the overlaps or remove them. The buffer
operation creates a new polygon data set Examples of Buffer
Bolstad, 2005 Examples of Buffer So, we really have the same data
in both Arc/Info and Idrisi. The Arc/Info coverages are vector,
while the Idrisi layers or images are raster. This slide shows the
result of a buffer.In Arc/Info I buffered the roads by 200 units
(meters). I used 200 meters as the buffer distance in Idrisi as
well. [DISCUSS Z-values with Idrisi] Clip or Window The Arc/Info
Clip command extracts part of a coverage using a polygon cookie
cutter coverage.To obtain the results shown on the left, I used the
roads coverage the Cookie coverage as the cookie cutter polygon.
The Idrisi output on the right is the result of using the Window
command.I simply supplied the column and row numbers describing the
Cookie layer and created a layer called Clip_Rd. [VIEW NEXT PART OF
SLIDE] As I mentioned earlier (Intro GIS) often times the most
important part of a spatial analysis technique is not the graphic
output, but the tabular output. Lets take a look at the table
created by Arc/Info for the clipped coverage. [essentially the
samejust extractednew length calcs, etc]. Overlay Another common
spatial analysis tool
Allows the user to identify areas where features in two layers
overlap. A new data set is often created from these overlaps. In a
Union Overlay, all features are included in the new data set but
the features that overlap represent a new feature. In an Intersect
Overlay, only the areas that overlap are contained in the new data
set. Overlay Example Analysis Tools select Overlay Intersect
tool
Union tool Examples Bolstad, 2005 Overlay Example - cont. Vector
overlay Bolstad, 2005 Overlay Example - cont. Raster overlay Other
Overlay Tools Erase Identity Symmetrical Difference Update
There really is no Identity type of command in Idrisi. In Arc/Info
this command is often used to identify the polygon found at a point
location (or series of points).I used this command to identify the
vegetation class at each live elk, killed elk, and random location
in my graduate research. This command could also be used to
identify the zoning at points throughout a cityor the soil
associations at sample points. Arc/Info Point coverage Polygon
coverage What type of polygon is found at this point location?
Boolean or nominal values (overlay polygon coverage and point file)
Polygon coverages for the layers should be overlaid on a point
coverage of the grid cell centroids using an overlay process using
Identity command in ArcGIS, to assign the environmental or planning
geography to each cell in grid. Generally, planning and political
layers are dealt with in this fashion. Fractional/Percentage values
(overlay polygon coverage and grid cell coverage) Polygon coverages
for the layers should be overlaid on a grid cell coverage using an
overlay process using Identity command in ArcGIS, to determine the
areas of environmental or planning geography in each cell in the
grid. These areas can then be summed by grid cell and be used to
calculate the percentage of grid cell covered by a particular
geography. Generally, environmental layers are dealt with in this
fashion. Near or Distance The Arc/Info Near command is used to
determine the distance or proximity of all points in a point
coverage to point, line, or polygon features in another
coverage.Once again, the important information is given not in the
resulting geographic features of the new coverage, but in the
database table. [Describe] [SHOW NEXT PART OF SLIDE] The equivalent
command in Idrisi is the Distance command.Idrisi produces a
distance layer with Z-values representing the distance of each
pixel to the nearest feature pixel (a pixel having a Z-value
>0). Distance Operation Dissolve Dissolve functions primary
purpose is to combine like features within data layers into new
feature Merge adjacent polygons with same attributes. DISSOLVE We
talked about the Arc/Info Dissolve command last week.The syntax of
this command is given here. [Clarify if needed]. In your Arc/Info
exercise this week (Ch. 8) you will be practicing with most, if not
all, these commands.Therefore, I will let the textbook lead you
through the process.However, try to remember what each technique is
trying to accomplishin other words, refer to this weeks and last
weeks presentations regarding spatial analysis. In addition,
remember that most of these Arc/Info commands will require three
parametersIN FILE, COOKIE or OPERATOR FILE, and OUTFILE. Since we
are not using an Idrisi text book, I will show you how to use these
techniques, so you can complete this weeks Idrisi exercise. Are
there any questions about the concepts I presented here? Bolstad,
2005 With Spatial Analysis Tools Use What You Can Do?
Find suitable locations. Find the best path between locations.
Perform distance and cost-of-travel analyses. Perform statistical
analysis based on the local environment, small neighborhoods, or
predetermined zones. Generate new data using simple image
processing tools. Interpolate data values for a study area based on
samples. Clean up a variety of data for further analysis or
display.