NR 143 Study Overview: part 1 By Austin Troy University of Vermont Using GIS-- 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 Unique values What are symbol styles? What is normalization? Introduction to GIS What are different methods for choosing class intervals? What are the tradeoffs?

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? Introduction to GIS