Editing and Analysis
Notes on Editing
• We have covered feature editing
• But not table editing
Creating New FC
• Biggest problem is remembering that
the EDIT button is where you set the
spatial reference for new empty FCs.
New, empty FC table
• When creating a new field in a table
– If you are using float or Double real
numbers then you have to specify
Precision and Scale.
• Precision = number of digits
• Scale is number of decimals
• 456.56 has P=5 and S=2
• As I said before, this is actually a
complex subject if you want to dig
into it see on-line help.
Tables can be edited…
•
•
•
•
•
While in edit mode
And
While not in edit mode
But the behavior is different
And this can be a major pain because
sometimes you have to keep switching
back and forth!
Some Table Option functions
FUNCTION
Edit mode NOT
EDIT MODE
Select by attribute
X
X
Clear selection
X
Switch selection
X
X
Select All
X
X
Add field
X
Add table to layout
X
X
Print table
X
X
Export table
X
X
Format table
X
X
Default table fields (min width)
X
X
Field Operations
• Rt click on column head and you get
• And a warning if you are
not in Edit mode
• So?
• Summarize - table
• Stats – table & graphic
• Turn field off – where
do you turn it back on?
Booby traps
• If you calculate fields the calculation
will only be done for selected rows IF
any rows are selected.
• There is a check box that controls
this but usually you want this
behavior
Analysis
• Starts with selection…
• Why?
• Because
– Many steps in analysis are simply selection by
• Attribute
• Location
– Most of the OVERLAY functions’ operations
depend on what features are selected
Booby Traps
• Selection is full of booby traps
• Most due to careless implementation
– Wrong files (dialog remembers)
– Wrong operation in Select by Location
– Building complex operations in either query
• Too many ANDs and Ors – logic not arithmetic
• Messing up AND and OR – too complex
– The Intersect function in Select by
location does not give the same results as
Intersect in Overlay Analysis
– Building complex operations in either query
• Too many ANDs and ORs – logic not arithmetic
• Messing up AND and OR – too complex
– a AND (b OR c) = (a AND b) OR c
– a AND (b OR c) =(a AND b) OR ( a AND c)
– Beginners – carry out each operation separately
and study results!
– This means you build up a bunch of layers so you
have to name them carefully!
– And you have to pay attention to what you are
selection from!
Booby Trap
• Select by location using Intersect
does not give the same results as
Overlay Intersect
Overlay Intersection
• BUT THE RESULT IS VERY DIFFERENT!
Red outlines
are the parcels
selected by
Select by
Location
Intersection
Green are the
result of the
Intersection
Overlay