Once a GIS layer is created, its attribute file can be linked (joined) to external data files. Joining is one of the most frequently performed data file processes because it brings together feature attributes that are contained in multiple digital data files. To perform a join, a unique matching field, the key identifier, must be observed in both data files.
★ Loading the external file that you wish to join to the GIS attribute file.
★ Selecting the external file and the GIS attribute file that you wish to join.
★ Selecting the field (containing the key identifier) in each file, and when joined.
★ Making sure that the join was successful.
Comma delimited, also known as comma-quote delimited and CSV, separate fields by commas. Character fields may be enclosed in double quotes, and need to be if they contain an embedded comma. Two commas in a row signify that the field is blank. Usually whitespace is not allowed before or after fields (although this may be tolerated in the CSV form).
Sorting temporarily rearranges your data file records, so you can view, select, update, or print them in the new sorted sequence. Although the specifics vary by program, you generally choose the field (or fields) you want to sort by. The first sort field arranges, usually in ascending or descending order, the records based on the field's contents. For example, a class roster might be sorted alphabetically by last name. Some systems allow you to choose a second sort field (or more), which arranges records (in ascending or descending order) when two or more records have the same first field value. If your alphabetical list has four students with the last name Maria then those four records could be rearranged in alphabetical order based on their first name.
Spacequote delimited ASCII is a variant of whitespace delimitation, but the attributes containing multiple words are enclosed in double quotes, and consequently, they can contain embedded spaces between words.
White-space delimited ASCII files differentiates fields by the use of one or more spaces. Since spaces separate fields, fields that have no value must be represented by a non-blank code and character attributes cannot contain spaces between words (underscores can be used to separate words). You can open ASCII files in any word processor or text editor.
You can delete a single record or a group of records in a data file by first selecting them and then deleting them. Since records are the database representation of features, when you delete records in the attribute file, you are also permanently discarding their spatial representation. The entire feature, graphic and record, is deleted.
Fields define feature attributes. Most GIS programs provide a way for you to add or delete fields from within your open data file. GIS program will instruct you to define a new field. You will give it a name and select from options that determine the data format of the values that will be placed into the field. Deleting a field usually involves selecting the field and deleting it.