Shapefiles (ArcGIS 10.1)
Introduction
The ArcGIS program group utilizes shapefiles to build up GIS layers. Shapefiles are createdand set-up in ArcCatalog. They are manipulated and modifiedin ArcMap and in ArcTools.ArcCatalog and ArcTools may be launched from inside ArcMap or as independent, stand-alone programs.
Shapefiles are found in ArcCatalog by expanding the Catalog Tree on the left side of the desktop and come in 3 main and 2 specialized types.
An individual shapefile is actually a group of five to seven individual files. Here is the Alteration 12-8-2011 shapefilesubfile group. Note this file is displayed as a single file in ArcCatalog and 7 files in Windows Explorer.
A shapefile will fail to load in ArcGIS if one of the critical subfiles is renamed or missing as may occur if a shapefile is zipped up in Windows Explorer and transferred to a different computer.
Shapefile Types
The three main shapefile types are point, polyline and polygon. The two specialty shapefile types are multipoint and multipatch.
Main Types / Use / ExamplesPoint / Point / Geochemical samples, drill hole collars, bedding attitude measurements.
Polyline / Lines / Contacts, faults, contours, roads.
Polygon / Areas / Outcrops, watersheds, claims.
Specialty Types / Use / Examples
Multipoint / Geoprocessing / Buffers, clips, unions.
Multipatch / Surfaces, Volumes / Topography, 3-D solids, 3-D planes.
Different shapefile types work seamlessly together in a GIS but an individual shapefile cannot contain mixed data types. A point shapefile may not contain polyline or polygon portions or any other combinations thereof.
Under certain circumstances it is possible to convert shapefile types: points can be joined to form polylines and so forth.
Creating Shapefiles
Shapefiles may be created in two ways. Primary shapefiles are created in ArcCatalog via wizards and populated using the editor function in ArcMap. Secondary shapefiles are converted from other file formats. This tutorial concerns the creation and set-up of primary shapefiles.
Creating Primary Shapefiles
Inside ArcCatalog, highlight the folder in which the new shapefile will reside and right-click the mouse. Go to New and then Shapefile on the drop-down lists.
The New command may also be accessed from the File dropdown list on the main taskbar, top-left on the desktop.
Change the name to Attitudes. Leave the Feature Type set to Point.
The new Attitudes shapefile is listed on the contents window to the right. The icon with three dots indicates that it is a point shapefile. Polyline and Polygon shapefiles are created with the same wizards, changing the feature type from point to polyline or polygon respectively (see Page 5).
Populating Shapefiles-Setting up the attribute table.
Primary shapefiles are empty shells and data must be added to them using the edit function in ArcMap after appropriate fields are added to the features attribute table.
Highlight the new shapefile and right click the mouse and select “Properties” on the pop-up menu.
Select the Fields tab and move the mouse cursor to the first blank Field Name line.
Field names will be the column headings in the shapefile attribute table. The right hand column, labeled Data Type defines what sort of data goes into each field. Data type “Text” is text shorter less than 255 characters. Memo is text longer than 255 characters. Numerical data types are integer, long integer, double and float. The last data type is date-no explanation needed.
Fields are added by typing in the new field name and then tabbing over to the Data Type field. Data type is selected from a pull-down menu accessed when the blank field is selected with the mouse. Close the window by clicking Apply and OK.
The new empty shapefile may now be added as a layer in ArcMap and is ready for editing.
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