FAQ: How Have Shapefile dBase Field Mappings Changed?

Answer

Changes in dBase\Shapefile Field Mappings

When creating a shapefile, the requested field types are mapped to ensure the data can transfer to other data formats and into ArcObjects without overflow or truncation. Because of this, there is no guarantee that the requested field type will be created. The "best fit" is created to eliminate any chance of data loss.

The field mapping used with dbase\shapefiles was changed, beginning at ArcGIS 10.3.1, to resolve a data truncation problem. In short integer fields, numbers like -12345 would be truncated to -1234. In long integer fields, numbers like -1234567890 were truncated to -123456789. The numbers are stored in the dBASE file as text and there is no allowance made for negative numbers. The excess precision was truncated without warning or error.

The mappings are enforced on creation and on insert/update by ArcObjects, arcpy, and through the user interface. Existing shapefiles are not changed and maintain their mappings. Operations that create new shapefiles use the new mappings. Performing a copy/paste operation on a shapefile is a file-based process and does not update the mappings.

Field Mapping in ArcGIS 10.3 and earlier versions

Type Offered on Create	Displayed in properties	Width	Precision	Min/Max Values Allowed
Short	Short	1-5		-9999*, 32767
Long	Long	1-10		-999999999**, 2147483647
Float	Float	1-6	1-6	-3.4028234664e+38, 3.4028234664e+38
Double	Double	7+	0+	-1.7976931348623158e+308, 1.7976931348623158e+308
Text	Text	1-254		254
Date	Date	10

* The min value that can be entered without truncation is -9999. A true short integer has a min of -32768.

** The min value that can be entered without truncation is -999999999. A true long integer has a min of -2147483648.

Field Mapping in ArcGIS 10.3.1 - 10.6

Type Offered on Create	Displayed in properties	Width Requested	Width	Precision	Min/Max Values Allowed
Short	Long	1-5	5		-9999, 99999
Long	Long	1-10	10		-999999999, 2147483647
Float	Float	n/a	0	0	-3.4028234664e+38, 3.4028234664e+38
Double	Double	n/a	0	0	-1.7976931348623158e+308, 1.7976931348623158e+308
Text	Text	1-254	1-254		254
Date	Date	10	10

At ArcGIS 10.6.1, Esri added support for scale and precision. Shapefile dBase field mappings have been changed both on creation and when viewing older files. This change was made to minimize data loss, which occurred under the previous mapping. If the precision is not specified or set to a length of zero, a Short integer defaults to Long(5) and a Long to Long(10).

Please note that in existing data, the internals do not change; only the interpretation has changed.

Field Mapping in ArcGIS 10.6.1 and later versions

Type Offered on Create	Displayed in properties	Width	Precision	Min/Max Values Allowed
Short	Short	1-4		-999*, 9999
Long	Long	5-10		-999999999**, 2147483647
Float	Float	1-7	1-7	-3.4028234664e+38, 3.4028234664e+38
Double	Double	8+	0+	-1.7976931348623158e+308, 1.7976931348623158e+308
Text	Text	1-254		254
Date	Date	10

* The min value that can be entered without truncation is -999. A true short integer has a min of -32768.

** The min value that can be entered without truncation is -999999999. A true long integer has a min of -2147483648.

Reading existing data

When reading existing data, the best fit to the new mapping is attempted. Nothing changes in the data, but the field type may be reported differently. Precision and type are used to determine the mapping, and precision/scale are displayed on preexisting shapefiles.