Inside joins o The records of the feature classes are joined based on whether

# Inside joins o the records of the feature classes are

This preview shows page 2 - 4 out of 13 pages.

Inside joins o The records of the feature classes are joined based on whether one feature is inside another State capitol example Outside joins o Use a proximity criterion to link one feature and its attributes to another EX: you want to know which bar is within 1 mile of every university in Washington Be sure to use a projection that preserves distance Describe the difference between simple and summarized spatial joins, and describe how this related to the issue of cardinality (7.1). Simple spatial joins o Used in one to one or many to one relationships o Ex: state capitol example o Ex: works for linking bars in U district to the school within one mile of them. This only works because there is only UW Summarized spatial joins o For one to many relationships o What happens is you summarize the info from the source table and attach that summary to the feature in the destination table. o This summary has many mathematical forms Sum Mean Median Minimum
Maximum o We use the summarized spatial join to ask how many (sum) bars are within one mile of all universities in Washington state. Describe geographic research questions that could be answered by various forms of spatial joins (7.1). Describe how buffering operations work, along with related concepts such as dissolve functions, multiple distance buffers, the importance of projections that preserve distance, etc. (7.2). Buffering operations create a new layer/polygon Creates a zone that is a distance that has been specified Dissolve all means to make one buffer for all instead of a bunch of overlapping buffers It is important to use projections that preserve distance because we don’t want things inside or outside of the buffer that is not supposed to be. Describe the different types of overlay operations (7.2). Overlay operations o The combination of spatial and attribute data from two or more spatial layers o What is on top of what? We use overlays to answer these types of questions o Vector overlay Overlay functions split features in an input layer where they are overlapped by features in the overlay area to produce a new vector layer All layers must be in the same projection Neither the input nor the overlay layers are altered Can work with points, lines, or polygons as the input layer The simplest kind of overlay is visual inspection but it is not a spatial operation Real overlay operations create a new layer There can be changes to both spatial and attribute data There are two main types of vector overlay operations Recombination o The attribute tables of two layers are joined together Intersection Selects out the areas that are common to both layers and attaches attributes from both layers to the output layer The snail tutorial o Its where these things occur Union Incorporates all areas from both layers and attaches attributes from both layers to all features in the output layer

#### You've reached the end of your free preview.

Want to read all 13 pages?

• Fall '08
• Staff