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General procedure for creating new feature themes by importing spatial ASCII data

A geographic feature is characterised by its location and descriptive attributes. INSROP GIS can create new feature themes by importing spatial data stored in delimited ASCII table files. The steps involved when importing spatial ASCII data are as follows:

1. Select type of spatial feature to create

2. Select input file

3. Select delimiter

4. Select spatial co-ordinate units

5. Specify output shapefile name

6. Specify the ID attribute and number of other attributes to include

7. Confirm whether the file columns are defined in headerline(s)

8. Specify which columns comprise the X and Y co-ordinates

9. Define attribute field names and specify the fields

10. Read the input file and create the features

These steps are further described in the following:

Select type of spatial feature to create

The spatial features may be points, multipoints, lines, multilines, polygons, multipolygons or "routes". The "route" feature type is not the same as an ARC/INFO route. The user is prompted to select one of these feature types.

Select input file

The user is presented a file selection dialogue window, and must navigate the folder tree to find and select the proper ASCII file.

Select delimiter

The ASCII files specifying the co-ordinates and attributes of the spatial features include this information in delimited columns. As delimiter, comma, semi-colon or space may be used. Two commas or semi-colons in a row are interpreted as an empty column value. Hence, there must never be more than one comma or semi-colon between each column, unless the column value really should be empty. There can also not be more than one type of delimiters in each file. If a comma or semi-colon is used as delimiter, any spaces on either side of the delimiter are ignored.

Select spatial coordinate units

The input data may be stored as decimal degrees (DD), degrees and minutes (DM), degrees minutes and seconds (DMS), or some projected co-ordinates. Input co-ordinates stored as degrees and minutes or degrees, minutes and seconds will be converted to decimal degrees.

Specify output shapefile name

The user is presented a file creation dialogue window, and must navigate the folder tree to find and select the proper storage location and specify the file name. An existing file may be selected (and overwritten) if the file is not in use.

Specify the ID attribute and number of other attributes to include

Although not strictly required by ArcView, the INSROP GIS development team has found it useful to require that an ID be assigned to each spatial feature. In most cases this ID is just a serial (integer) number, but it may also be a character string. In principle the ID may also be e.g. a location name, but we recommend that the ID attribute is kept short. For string IDs the table field is created as a variable-length character field, and the user is prompted for maximum number of characters in the string. For number IDs the table field is created as a LONG integer field.

The specification of the ID attribute includes "ID-column label", "ID-column #" and "ID-type (String/Number)", and the user is prompted for these values. The default values are:

<string in column #1 of first line in ASCII file>,

"1",

"N",

which means that the the IDs are stored in column #1 in the ASCII file and consist of Integer values. The ID column does not have to be the first column, but all columns to the left of the ID column are ignored.

In addition to the specification of the ID column, the user is prompted for the number of attributes to include in the created shapefile. The default value is the number of attributes INSROP GIS has identified in the ASCII file, but the user may specify a smaller number if some of the rightmost attribute columns should be ignored.

Confirm whether the file columns are defined in headerline(s)

The user is prompted to confirm whether the ASCII file column names are included in headerline (s).

Specify which columns comprise the X and Y coordinates

The spatial co-ordinates must be in two sequential columns, but it doesn't matter whether the X- or the Y-co-ordinate column is the first of the two. For geographic co-ordinates the longitude (+ = East) represents the X co-ordinate and the latitude (+ = North) represents the Y co-ordinate. If the ASCII file includes a headerline with N and E included in the two co-ordinate column names (i.e. North and East), INSROP GIS use this to determine which co-ordinate columns include which co-ordinate. If not, the user is prompted to specify the column numbers for the two co-ordinate columns.

Define attribute field names and specify the fields

If the ASCII file comprise a headerline, the attribute field names are read from the headerline, and the user is prompted for the type of each attribute. If not, the user is prompted for attribute table field names and specifications. For decimal and string attributes, the user is also prompted for some additional field specifications.

Read the input file and create the features

Based on the given user input, the ASCII file is read and the shapefile created. During this process the system checks that line features are defined by a minimum of two points and polygon features by a minimum of three points.