Tuesday, April 15, 2014

Creating regions in ArcMap after polygons are built

Use this procedure to make a multipart polygon from independent polygons that are already digitized.

1) Open the Editor toolbar and start editing.  (If the Start Editing window appears,
choose the directory source which contains the shapefile to be edited.  The desired
shapefile must be resident within the TOC.)

2) Within the Editor toolbar choose the shapefile to be edited within the Target window.

Read more ...

Monday, April 14, 2014

Polygon-Raster Overlay

A procedure for generating a raster whose cell values reflect the sum of
the area of polygons in a shapefile that fall within each raster cell

Input for this description is a single shapefile of land use identified
as "la93_org.shp"

Assume: 
- the data frame, and operations, will be in UTM, Zone 11 projection
- the output raster cells will be 5km x 5km
- the extent of the raster is:
     top: 3726519.06
     left: 423994.79
     bottom: 3711519.06
     right: 438994.79
- the raster, based on cell size and exent, will have 3 x 3 cells  
   (this is small intentionally for demo purposes)
Read more ...

Sunday, April 13, 2014

How to Scan and Digitize

How to Scan and Digitize
------------------------


One-Time Setup
--------------
decide what format to scan documents (e.g., png, jpg) and what resolution (e.g., 300 dpi)
define where to store scanned documents, digitized layer files (shapefiles) and raster files
decide what raster file cell size to use and in what distance units
decide what projection to use (e.g., equal area)
generate base grid that encompasses the project area (e.g., the World)
clip out sub-areas for local data creation and analyses (e.g., a Continent)


Read more ...

Saturday, April 12, 2014

A procedure that extracts the minimum value of an attribute of all points and populates the associated cell of a raster with the minimum values.

What this recipe does
---------------------
Convert a raster file so that the cells of the
raster are converted to a smaller size.  This procedure,
known as "resampling", also can be performed on a raster
to generate cells that have a larger size.

What you will need
------------------
ArcGIS (ArcView level)
Spatial Analyst Extension


Read more ...

Friday, April 11, 2014

downloading GTOPO30 data, extracting the data then processing within ArcGIS

Go to:
  http://edcdaac.usgs.gov/gtopo30/gtopo30.html

Click on the desired quadrant then download the data file
(e.g., e140s10.tar.gz) to a Unix computer.

Then type "gunzip e140s10.tar". This will generate the
"e140s10.tar" file.

Read more ...

Thursday, April 10, 2014

How to genereate a lattice polygon covering a continent

This procedure is useful for Brad Hawkins' project wherein
we want to make a rectangular lattice of polygons over the
continent.

Assume there is a polygon shapefile for the (North American) 
continent called (e.g., "newcontinent") that has an short or 
long field, e.g., "ShortField" (cannot use real or string).  
The values in this field are not relevant.  The polygons in the 
shapefile must be only those of the continent to be processed.  
Delete any island polygons or other continent land polygons.
Read more ...

Wednesday, April 9, 2014

Assigning point values to raster cells


What this recipe does
---------------------
Given a point shapefile with diverse values from which you want
to extract minimum and maximum (or other statistic) values,
perform an analysis that, on a cell-by-cell basis, extracts
the minimum value of an attribute of all the points for
each grid cell and populates the associated cell with the
minimum values.  Do the equivalent for maximum values of
the point attribute.


Read more ...