GIS Conventions¶
Shapefiles¶
We work with QGis , a widely used open source, free software for working on maps and geographical data.
Shapefile is a standard file format for mapping, that Gisaf can import. QGis can open and save shapefiles.
We have defined some simple norms about these shapefiles for integration with Gisaf.
Coordinate system¶
We use CRS SRID 32644.
Column (attributes)¶
- All objects in a shapefile (layer) have a unique identifier named "id": numerical value.
Field (attribute) names¶
- All fields are lower case (
UpperCase, use:lowercase)
- They do not contain spaces, but underscores (
not this, use:but_that)
- The field names cannot have more than 8 characters (
this_is_too_long, use:this_short)
Attribute types¶
- The dates are written in ISO format:
YYYY-MM-DD(eg.1968-02-25)
Fields to remove¶
- Eventually, remove the fields containing the coordinates: northing, easting, elevation, latitude, longitude, area, length, etc (these might be present when the data is imported from speadsheet)
Foreign keys¶
We often deal with labels or categories of objects in a layer.
A common use case to explain: Alice creates a layer of stones, and wants to tag each stone with a rating: these are picked from a list of choices, like: Beautiful, Interesting, Pretty, etc.
For these kind of attribute: define a column like rating_id (something ending with _id) as a numerical value, and assign values 1, 2, 3, etc. The text is defined in another table (typically a CSV file), that looks like:
| id | name |
|---|---|
| 1 | Beautiful |
| 2 | Interesting |
| 3 | Pretty |
Code¶
We have defined a standard set of codes, that defines the type of data. They can be found here (TODO: add link).
Add a column code_name, matching with one the code, eg. V25 for TDEF.
Surveyor¶
We keep a record of the people who realized the surveys (the surveyors).
The shapefiles must contain an attribute srvyr_id, which refers to this table (TODO: add link).
Accuracy¶
We keep a record of the accuracy of the surveys.
The shapefiles must contain an attribute accur_id, which refers to this table (TODO: add link).
Date of survey¶
As nothing is absolutely permanent, it's also important to keep track of the date of the surveys: the shapefiles must contain an attribute date.