Transcript Introduction to GIS - University of Vermont

------Using GIS-Introduction to GIS
NR 143 Study Overview: part 1
By Austin Troy
University of Vermont
Introduction to GIS
What is this overview?
•A general review of the major concepts we touched
on during the semester, with information on what
you’re responsible for in the exam.
•It includes materials from before and after the
midterm
Introduction to GIS
Data Structures/Models
•Vector
•Raster
•Strengths and weaknesses
•Usages
•Tradeoffs
•Tossups
Introduction to GIS
Vector data model
•Vector features types—points, lines polygons
•How are they made?
•Topology
•What are advantages?
•How does a topology table work
•What is spaghetti data?
Introduction to GIS
Legend editing—displaying
attributes
•How do we represent quantities and
categories geographically?
•Graduated color
•Graduated symbol
What are different methods for
choosing class intervals? What
are the tradeoffs?
•Unique values
•What are symbol styles?
•What is normalization?
Introduction to GIS
Database concepts
•What are the major data types? Number, text, etc.
•What are some different number types? Integer, double
precision, currency, etc.
•How does numeric data type relate to precision?
•What’s the difference between an 8 and 16 bit number?
•What is the difference between numeric and text data
types?
•What’s the difference between storing a number as text
and as a number type?
Introduction to GIS
Database concepts
•What are the major database models: Hierarchical,
network and relational
•How does each work?
•Why is relational superior?
•What are fields, records, keys and cells
•What is the difference between a one-to-one and many
to one or one to many relational database?
•What are tabular joins? Why does data type matter for
them?
Introduction to GIS
Queries
•How do queries work?
•What are logical operators and how are they used to
define queries?
•What’s the difference between single and multiple
criteria queries?
•How are text queries versus number queries different?
Introduction to GIS
Queries
•What’s the difference between the AND and OR
operators?
•What’s the difference between “new selection,” “select
from current selection,” and “add to current selection?”
•How do these methods relate to AND and OR queries?
•What can we do with selections once the query is run?
•Statistics, export to new theme, run calculation
•How can queries be combined with calculations to
create new attribute fields.
Introduction to GIS
Spatial queries
•Also known as select by location
•What kind of multi-layer queries can we do?
•Select points or lines that fall within polygons,
•Select points or lines within a certain distance of a
point line or polygon
•Select polygons that fall either entirely or partial
within a polygon in another layer
•Can set rules for partial coincidence, like having
centroid within the polygon
Introduction to GIS
Spatial joins
•How we attach attribute data from features in one layer
to overlaying features in another layer.
•How do we assign distances using spatial join?
•For line to line, line to point, point to line and point
to point operation, always gives a distance
•For polygon to point, we must specify this option
•Creates new attribute representing distance for each
feature in layer A to nearest feature in layer B.
Introduction to GIS
Spatial joins
•Why is spatial joining of two polygon layers more
complicated?
•Because they likely have different geometries
•What can we do about that?
•ArcGIS allows us to take average of values of the
overlapping polygons.
Introduction to GIS
Vector geoprocessing
•Why does it allow us to answer geographic queries
more accurately than just selections?
•Allows us to create smaller minimum mapping unit to
show a smaller, more accurate representation of where
our criteria are true
•Geoprocessing also allows us to aggregate features
into bigger features and create new features through
buffering
Introduction to GIS
Vector geoprocessing tools
•Break down minimum mapping unit into smaller unit:
•Union
•Intersection
•What is the difference? How do they relate to AND
and OR?
•Making bigger features
•dissolve
Introduction to GIS
Vector geoprocessing tools
•Tiling two or more layers together
•Merge
•Reducing the extent of a layer
•Clip
•Creating a new polygon around a feature
•Buffer
Introduction to GIS
Vector geoprocessing tools
•How can we combine geoprocessing tools in order to
ask spatial queries that involve attributes in a number of
different layers?
•See lab 6
Introduction to GIS
Scale and extent
•What is the difference between large and small scale?
•What does a numeric scale factor (e.g. 1:100,000)
represent?
•What is map extent and how is it related to scale?
•How is vector representation linked to scale? When do
you stop using lines and points to represent things and
start using polygons and why?
Introduction to GIS
Raster
•What are raster queries and raster calculations?
•What’s the difference between a multi layer and single
layer raster query or calculation?
•What outputs do raster queries and calculations yield
• How do we use raster queries to look for areas that
meet certain criteria from different layers?
Introduction to GIS
Raster
•What is the tool that allows us to summarize raster
values by a polygon or line? Zonal statistics.
•How does it summarize those raster values?
•What is a distance grid and a proximity grid?
•How do we make calculations for a window of cells?
Neighborhood statistics? What is the output?
•What is the difference between a low pass and high
pass filter using neighborhood statistics? Which one
smoothes a surface and which accentuates change?
Introduction to GIS
Raster
•What’s the difference between using a big
kernel/window for neighborhood statistics and a small
one?
•How does viewshed analysis work? What are the
inputs and outputs?
Introduction to GIS
Interpolation
•This is how we guess at attribute values in between
known sample points
•What types of values might we interpolate?
•What condition needs to be met to run interpolations?
Spatial autocorrelation/ spatial dependency. Values
cannot be spatially independent.
Introduction to GIS
Interpolation
•Why does the density of sample points matter?
•What is the importance of getting a representative
sample and why might we want variable sampling rates
across space to get that?
•What do we call it when we have different sampling
rates across some factor, such as space: stratified random
sampling.
•What’s the relationship between scale and interpolation?
•What is a density function and how is it different from
interpolation?