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 (<) Greater 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 from an 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. Let’s take a look at the table created by Arc/Info for the clipped coverage. [essentially the same…just extracted…new length calc’s, 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 city…or 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 function’s primary purpose is to combine like features within data layers into new feature Merge adjacent polygons with same attributes. DISSOLVE <IN> <OUT> <DISSOLVE ITEM> 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 accomplish…in other words, refer to this week’s and last week’s presentations regarding spatial analysis. In addition, remember that most of these Arc/Info commands will require three parameters…IN 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 week’s 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.