Basic Usage Tutorial

Tutorial Requirements

In this tutorial we are working with a data set of Wellington City building outlines, published by Land Information New Zealand. You should be familiar with basic terminal commands and QGIS editing functions.

Create or choose an empty folder for this tutorial and copy the example GeoPackage into your tutorial folder. For example:

$ ls
wellington-building-outlines.gpkg

Creating a new Repository & importing data

Kart makes it possible to store spatial and tabular data in a version controlled data repository.

Decide on a path to your new repository. To create the repository and import the table, use the init command. Since there is only one table in the GeoPackage, wellington_building_outlines, you don’t need to specify which table to import.

$ mkdir buildings-project
$ cd buildings-project
$ kart init --import=GPKG:../wellington-building-outlines.gpkg
Starting git-fast-import...
Importing 75,408 features from GPKG:../wellington-building-outlines.gpkg:wellington_building_outlines to wellington_building_outlines/ ...
Added 75,408 Features to index in 2.6s
Overall rate: 29198 features/s)
/Users/me/code/kart/venv/libexec/git-core/git-fast-import statistics:
---------------------------------------------------------------------
Alloc'd objects:     125000
Total objects:       120522 (         0 duplicates                  )
      blobs  :        75431 (         0 duplicates      73930 deltas of      73936 attempts)
      trees  :        45090 (         0 duplicates          0 deltas of          0 attempts)
      commits:            1 (         0 duplicates          0 deltas of          0 attempts)
      tags   :            0 (         0 duplicates          0 deltas of          0 attempts)
Total branches:           1 (         1 loads     )
      marks:           1024 (         0 unique    )
      atoms:          75691
Memory total:         26402 KiB
       pools:         18590 KiB
     objects:          7812 KiB
---------------------------------------------------------------------
pack_report: getpagesize()            =       4096
pack_report: core.packedGitWindowSize = 1073741824
pack_report: core.packedGitLimit      = 35184372088832
pack_report: pack_used_ctr            =          2
pack_report: pack_mmap_calls          =          1
pack_report: pack_open_windows        =          1 /          1
pack_report: pack_mapped              =   16667668 /   16667668
---------------------------------------------------------------------

Closed in 1s
Checkout to /Users/me/kart-tutorial/buildings-project/buildings-project.gpkg as GPKG ...
Commit: dd4d5159a020d1c7a661d6fe7a8e099a92cba7e1

Once the import is complete, you will have an initialised repository with your data imported. Check its current status:

$ kart status
On branch master

Nothing to commit, working copy clean

Working Copy

A working copy is a version of your data repository in a form you view and edit. Your working copy is a new GeoPackage with additional tracking information.

Normally your working copy is named the same as your project folder and is located inside your project folder.

In our example, in the buildings-project/ folder the working copy is named building-projects.gpkg.

Remember that the repository is the folder path buildings-project/. This is the location where you should run your kart commands to manage your repository, checkouts, branches, etc. The working copy is your tracked data - i.e. the data you can view & modify.

Open QGIS and find the tutorial folder in the file browser. Open buildings-project.gpkg and add the wellington-building-outlines layer to your map. QGIS will display the layer content.

../_images/basic-tutorial-1.png

Making and Committing Changes

A “commit” is another word for saving a change in your data to the repository. One commit can contain any number of changes - modifications, additions and deletions.

In QGIS, select the wellington_building_outlines layer and toggle editing on. Select a feature and open the attributes table and change a value. In this example, we select a stadium and modify the use from Unknown to Stadium.

../_images/basic-tutorial-2.png

Once you have edited the feature, save the layer edits and toggle layer editing off.

From your terminal, use kart status to see the effect of the edit.

$ kart status
On branch master

Changes in working copy:
  (use "kart commit" to commit)
  (use "kart reset" to discard changes)

  wellington_building_outlines/
    modified:  1 feature

kart reports a single modified feature. We can see the detail of the change with kart diff.

$ kart diff
--- wellington_building_outlines:fid=4381
+++ wellington_building_outlines:fid=4381
-                                      use = Unknown
+                                      use = Stadium

Once you’ve checked that the change looks correct, you can commit the change to the repository with commit. You need to provide a commit message - a human readable description of the change.

$ kart commit -m "Updated stadium usage attribute for the Kart usage tutorial."
[master 094b328] Updated stadium usage attribute for the Kart usage tutorial.
  wellington_building_outlines/
    modified:  1 feature
  Date: Fri Jun 19 12:11:40 2020 +1200

Your change has now been saved in the history of your repository. Running status will show the new ‘clean’ state of your working copy:

$ kart status
On branch master

Nothing to commit, working copy clean

Resetting Changes

Kart provides a simple method to undo the changes you’ve made since your last commit, called reset.

Switch back to your QGIS window. Toggle editing back on, select a large number of features and delete them. Toggle editing off in QGIS, saving the QGIS layer edits when prompted.

../_images/basic-tutorial-3.png

Now run kart status to see the effect of your edit on the working copy data:

$ kart status
On branch master

Changes in working copy:
  (use "kart commit" to commit)
  (use "kart reset" to discard changes)

  wellington_building_outlines/
    deleted:   199 features

Rather than save this edit, roll the data back to the previous commit with kart reset:

$ kart reset
Updating buildings-project.gpkg ...

In QGIS, press f5 or click the ‘refresh’ button. The layer will be updated to it’s previous state before the features were deleted.

../_images/basic-tutorial-4.png