Importing Grid Data

Text Size: S M L XL

This guide describes the steps for bringing raster data (in .txt file format) into ArcView and ArcGIS.

Rasters — such as images and grids — represent geographic features by dividing the world into discrete squares called cells. Cells are laid out in a grid, where each cell has a location relative to an origin and a value describing the feautre being observed — for instance, the cell values in an aerial photograph represent the amount of light reflecting off the earth's surface.

A raster can represent thematic data, such as land use and elevation; spectral data such as satellite images and aerial photographs; and pictures, such as scanned maps and building photographs. You will generally display thematic and spectral rasters as a background to other geographic data on your maps. (Using ArcMap; ESRI, 2000)

Grid and Raster Defined

A grid is a geographic representation of the world as an array of equally sized square cells arranged in rows and columns. Each grid cell is referenced by its geographic x,y location.

A raster represents any data source that uses a grid structure to store geographic information.

Importing Grid Data Using ArcView

Sample data set: GRCA Land Cover – landcov99.txt

1. Start ArcView.
2. Load the Spatial Analyst extension and open a new view.
3. From the File menu choose Extensions.

   

4. Click in the check box labeled Spatial Analyst and press the OK button.
5. In the project window choose View and click New to open a new view.
6. From the file menu click on Set Working Directory (e.g. c:\temp). This step establishes the path and directory where the imported files will be stored.

   

Import and Draw a Grid Theme

1. From the file menu select Import Data Source.
2. In the Import Data Source dialog box select import file type as ASCII Raster. Click OK.

   

3. Navigate to the directory where the grid data is stored. In the bottom left box, select All Files. Click on the grid file to be added and click the OK button.

   

4. In the Output Grid screen, the default file name is imgrd. Change this file name to something more meaningful.
5. In the Import Grid dialog box, click on Yes to have cell values as integers.

   

6. The image now draws as a view in ArcView.

   

   The colours of the display are easy to change, and specialized colour ramps are provided for common data such as elevation and land cover.

For more information using the spatial analyst in ArcView consult these books located in the Data Resource Centre:

• Using ArcView GIS
• Using the ArcView Spatial Analyst

Using ArcGIS

Sample data set: GRCA Land Cover – landcov99.txt

1. Open ArcCatalog

   Before bringing the grid into ArcMap, this text file needs to be converted into a supported data format.

2. On the main tool bar click on the redToolBox button to open ArcToolbox.

   

3. The tools in ArcToolBox are organized into four main toolsets. Expand the Conversion Tools tree and then expand the Import to Raster tree.

   

4. Double-click on the ASCII to Grid tool.

   

5. In the ASCII to Grid dialog box, in the Input ASCII file use the folder button to navigate to the grid file you want to add to ArcMap. Choose the grid type — Integer or Float. In the Output grid box, enter the path to where you are storing the grid. Note that the output grid name has no file extension. Click OK.

   

6. Return to ArcMap and add the grid.

Top

Visit

The DRC is located behind the Research Help desk in the McLaughlin Library.

Check DRC help hours

© 2012 University of Guelph Library
Guelph, ON, Canada N1G 2W1
519-824-4120 x53617

CourseLink Web Advisor GryphMail Learning Commons

Send comments