Point Tools 2014

transcript

http://nrm.salrm.uaf.edu/~dverbyla/nrm435

Overview of lecture/demo…in lecture I use Create Fishnet, Create Random

Points tools to create test data

Point, line or polygon layers will always have an associated attribute table.

Table rows are sometimes called records and columns are typically called

fields. Most of our layers will have one row of information for each layer

feature (point, line or polygon).

You can use the Delete Field tool to delete more than one field. Or open the

table, right mouse click on the field to delete

You can use the Add Field tool, or open a table in Arcmap and Add Field…

Use the field calculator to calculate field values for all table records or for

selecte records.

Right mouse click on a field, select Statistics…

The Summary Statistics Tool can be used to create a new table of summary

statistics for any fields by any categorical (case) field. In this example for each

different X category (X of 10 or 20), determine how many points there are in

each category and what the Field A min, max, and mean values are for each X

category.

You can visually select features, select feature based on an attribute question,

visually select table rows, or select features based on the spatial relationship

to another layer (points inside poygons, points within a user-specified distance

to lines, etc.

You can use the Select Features tool to graphically select points by delineating

a rectangle around the points.

By holding the shift key down, you can graphically select using more than one

rectangle.

You can query any theme based on field attribute values.

Use the “Get Unique Value” button to list unique values for any field.

If you like to use Model Builder or scripting, you can use the Select Layer By

Attribute Tool.

You can also use the Make Feature Layer tool or layer properties…Definition

Query so select features and then display only the selected features in an

Arcmap layer.

You can select to a new selection, add to already selected point features,

remove from a selection set of points,

Or select from a selection set of points.

You can also select records (rows) directly from the attribute table by

Holding the shift key down as you select rows. To clear selection, point to the

upper corner box in the table and

mouse-click on it.

You can do the same thing using the Select Layer By Location tool…you could

use this in Model Builder…

Many tools for asking distance questions are typically in the Proximity toolset

Create Thiessen Polygons create polygons representing the point the polygon

is closest to. You might use this with landing strip points to show a quick map

of the closest landing strip anywhere you are flying. Or if you had lightning

strike locations for interior Alaska and wanted to show areas of relatively high

densities of lightning strikes which would be represented by small thiessen

polygons.

In this example, if the output buffer polygons are from the sam sex value, then

dissolve the buffers together.

There are 2 key concepts with point buffers: dissolve, fixed versus field

buffers. The buffer output is ALWAYS polygons!

You can also use the Multiple Ring Buffer geoprocessing tool if you have more

than 1 fixed distance.

You can use the Multiple Ring Buffer script to create many buffers around

features. In this example the user requests buffers representing distances of

1,2,3, and 5.

Near, Spatial Join, Generate Near Table work with points, lines, and polygons.

Point Distance tool works only with point feature classes.

In this example, for each point find the distance the the closest stream and

store the distance and stream feature ID in the points table.

The Spatial Join tool has many more options, such as what fields are output,

what the name of the distance field is, etc.

The Generate Near Table allows you to search for the closest features for

more than one near feature class, and also allows to find more than the

closest, in this case we search for the closest two streams… the IN_FID is the

feature ID of each point, the NEAR_FID is the feature ID of each stream line.

Point Distance outputs a table of all possible point distances between 2 point

themes.

Clip for example, to keep points inside a watershed polygon. Erase for

example to delete points inside a new building polygon,

Intersect for example, the keep points inside each vegetation polygon and

transfer the vegetation information to each point.

The Clip tool allows you to output all features inside clip polygons to a new

GIS theme.

The Erase tool is the opposite of Clip…it outputs all features that area outside

of erase polygons to a new GIS theme.

The Intersect tool is the like Clip…but it also transfers all polygon attributes to

each point the polygon intersects with.

I will cover point density methods using interpolation to rasters later this

semester when we start with rasters.

In the feature world (points, lines, polygons) the question is how many points

are in each polygon.

To determine the density of lightning strikes in the Yukon Flats National Wildlife

Reguge, need to know area of refuge in km2 and number of strikes in the

refuge.

Compute the area in km2

And determine number of points inside refuge polygon: 4,294 strikes in

polygon

We make our sample squares using the Create Fishnet tool…

Fishnet does not cover all of refuge, so increase number of columns…

Compute the density in each square polygon using spatial join tool…

Symbolize the number of strikes in each fishnet polygon…

Clip using refuge polygon and compute density per km2…spatial join to get

count of strikes in each polyon

You could also visualize density using Thiessen polygons…

Point Tools 2014

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