The rest of the semester

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The rest of the semester

• 11/17 T - Lecture Geodatabases and raster
  analysis
• 11/20 F - Lab Group A work on Project 5,
  please bring class notes data all typed in
  (group B off)
• 11/24 T - Lab Group B work on Project 5,
  please bring class notes data all typed in
  (group A off)
• 11/27 F - Thanksgiving
• 12/1 T - In-class final
• 12/4 F - Review for practical (project 5 due)
• 12/10 Th - Timed lab practical exam
• group A 800am-925am group B 930am-1055am

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Geodatabases why bother?

• If you have related files, you can change
  something once (like the projection) and it will
  fix all of them
• It lets you put in defaults (for example if you
  are digitizing in roads and the default is paved,
  then you dont have to type in anything unless
  the road is unpaved.)
• Allows you to type in an acceptable ranges of
  data input (for example, if you are typing in zip
  codes and there are only 5 possibilities, you can
  type in these possibilities and then just select
  the right one)
• Topology - (so if you do an intersection, it will
  recalculate the area just an example!)

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Two types of GeoDatabases

• Personal
• Access
• Multi-user
• SDE

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Geodatabases
Feature datasets

• Related feature classes
• Common coordinate system
• May participate in topologic relationships and
  networks

Feature classes
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Create geodatabase
In ArcCatalog
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Design your own personal geodatabase.

• Come up with a group of data layers that you
  would want to have in a personal geodatabase.
  List 2 feature datasets and 2 feature classes you
  would have in each

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Setting up your geodatabase Spatial Reference

• Every data set requires a complete description of
  its coordinate system for proper display and
  analysis
• Geographic coordinate system / datum
• Projection (if one is used)
• Storage units used to store the x-y values
  (degrees, feet, etc.)
• Domain, or maximum allowable x-y values
• Resolution, or the x-y precision

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Setting up your geodatabase Tolerances

• During geometry operations (like buffering,
  intersect, editing, etc) tolerances are used to
  determine whether two features should be the
  same. The tolerance is the maximum distance a
  feature vertex can be moved to coincide with
  another vertex.

Coincident lines?
Tolerance
Clustering
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Default tolerance

• Set based on coordinate system units and is
  equivalent of 1mm
• 0.001 meter
• 0.003281 feet (0.03937 inches)
• 0.0000000556 degrees
• Give good results in most scenarios
• The XY tolerance always be smaller than your data
  capture resolution

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Setting up your geodatabase 3. how you do it
in ArcCatalog
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Importing feature classes Single or batch
tools Use SQL to select only certain
features Layer CS will be automatically projected
if different from the feature dataset CS
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New feature class to put in your geodatabase
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Cool stuff you can do with your new geodatabases
Using default attributes
Automatically assign default values as features
are added.
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Cool things you can do with your new
geodatabases Domains

• Rules for data entry
• Prevent typing errors
• Can verify that values fall into correct range
• Created for entire database
• Can be re-used in different feature classes

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Domain types
Range domain Percentage
Coded domain PipeSize
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Domain examples
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Domain uses
Save space by storing numeric code, but set up
domain for easy interpretation of values
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Creating domains
For coded domains
For range domains
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Your turn

• Choose one of your feature data sets
• List a potential field and alias
• List a good potential default
• Come up with a domain for that field
• Is it a range or coded domain?
• Give the range or codes

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Raster Geoprocessing Advanced Analyses

• For most of these you would need the Spatial
  Analyst extension for ArcGIS or another raster
  program.

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Review Advantages of vectors

• Precise location of features
• Storing many attributes
• Flexible for cartography
• Compact storage of information
• Ideally suited for certain types of analysis,
  especially areas, lengths, connections

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The raster data model
X, Y location
X, Y location
Columns
Rows
Raster data file N rows by M columns
Georeferenced to earths surface
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Impact of resolution

• Storage space increases by the square of the
  resolution
• Portraying large areas at high precision is
  problematic
• This 50mx50m grid size is fine for the top map,
  poor if you want to do a close up.

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Types of raster data
Continuous raster DEM
Discrete raster land use
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Continuous data

• Raster is the best way to store continuously
  changing values such as elevation
• Analysis faster and more flexible than vectors
  for many applications
• Some analysis only possible using rasters

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1. Example of things you can do with rasters
Local Functions. Can add, subtract, multiply,
divide, average, etc. individual cells.
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Another example of a local function
Precipitation data from rain gauges taken over 3
weeks. How much rain fell per cell total?
 
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What would day1day2day3 ?
 
You can then create contours and create a new
raster layer.
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2. Neighborhood Operations (also called focal
in manytextbooks) You compute a new value for
each cell in a grid as a function of the spatial
relationship between the focal cell and its
neighborhood. Neighborhoods are standard
shapes (squares, circles, ovals, etc)
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• Zone Operations.
• Zones represent 2-dimensional areas but
  unlike neighborhoods, can vary in size and shape.
  For example, the grid on the left will show the
  zones (in this case depth of water) and the grid
  on the right is the variable (in this case
  temperature). You may want to average
  temperature by zone.

Water Depth Temperature
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What would be the average temp in each cell?
24 24 54
75
24 54 54
75
24 54 54
75
     
24 54 54
75
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Advanced Analyses

• I
• DDigital elevation models (DEM) / digital terrain
  models (DTM)
• - - data layers where the attribute data is
  elevation
• - why arent they considered to be truly
  3D?
• tThey are called 2.5 D, because elevation is
  stored as an attribute rather than spatial data.
  Areas that are overhangs are problematic

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.
TINs
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Grid based DEM
2Grid DEMS  Each cell contains elevation
data Generally easier to work with than TIN, but
use a lot of computer space Better in areas with
more subtle changes in elevation
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• Which would be better in the Grand Canyon?

• Which would be better in St. Petersburg?

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Things we calculate with DEMS   1. slope and
aspect slope rise / run (or change in y axis /
change in x axis) aspect direction (N, S, E, W)
of the maximum rise or drop from the center  
Slope
Aspect
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2. Line of Sight Analysis In this case, red is
for tower 1, blue for 2 and green for 3
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3. drainage models   Using slope and aspect, we
can calculate flow of water. Assumes that water
flows only due to slope. What are some other
factors?
Drainage Model from DEM