Accessibility Analysis
=======================

🚑 How fast can you reach essential services?
--------------------------------------------

Accessibility analysis in RA2CE answers practical questions like:

- *What is the shortest route from home to work?*
- *Which is the quickest evacuation route to the hospital during an emergency?*
- *How far is the closest school, shelter, or service from each neighborhood?*

By analyzing **origin–destination (OD) routes**, RA2CE helps you explore connectivity
under both normal and disrupted conditions.

.. note::

   Accessibility analysis is built on the **origin–destination (OD) framework**.
   You provide one or more origins (start points) and destinations (end points),
   and RA2CE calculates the shortest or quickest route between them.

.. image:: /_resources/sint_maarten_accessability.png
   :alt: Accessability of population to health centers in Sint Maarten under flood conditions
   :align: center
   :width: 100%


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Preparing Origins and Destinations
----------------------------------

📍 Before running any OD analysis, you need to prepare two shapefiles:
one for the **origins** (start points) and one for the **destinations** (end points).

These shapefiles must follow a specific data structure so that RA2CE
can recognize them. For example, destinations can be grouped into
categories such as hospitals, schools, or shelters.

.. warning::

   If the shapefiles are not prepared correctly, the OD analysis will fail.

👉 For a full explanation of the required attributes and example files,
   see the :doc:`Origins and Destinations data preparation <accessibility.prepare_data_origin_destinations>`.


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Case 1: Defined Origin–Destination Pairs
----------------------------------------

In this mode, you provide a **list of specific origin–destination pairs**.
RA2CE then computes the shortest or quickest route for each pair.

Typical use cases:

- Checking travel time between specific towns or facilities
- Studying accessibility between fixed points (e.g. home → workplace)

👉 See the detailed tutorial: :doc:`Defined Origin–Destination Pairs <../_examples/accessibility_all_pairs_origin_destinations>`

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Case 2: Origins to Closest Destinations
---------------------------------------

Instead of defining pairs, you can let RA2CE automatically find
the **closest destination for each origin**.

Example:
For every household (origin), RA2CE finds the nearest hospital,
the nearest school, and the nearest shelter (destinations).

This is especially useful for:

- **Emergency planning** (finding the nearest hospital or shelter)
- **Service accessibility** (how close is the nearest school for each neighborhood?)

👉 See the detailed tutorial: :doc:`Origins to Closest Destinations <../_examples/accessibility_closest_origin_destinations>`

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When to Use Which?
------------------

- Use **Defined Origin–Destination Pairs** (Case 1) if you already know
  which specific locations you want to connect.
  Example: *“From school X to hospital Y.”*

- Use **Origins to Closest Destinations** (Case 2) if you want to automatically
  find the nearest service from each origin.
  Example: *“From every household/neighborhood to the closest hospital.”*

----


.. toctree::
   :maxdepth: 1

   accessibility.prepare_data_origin_destinations
   ../_examples/accessibility_all_pairs_origin_destinations
   ../_examples/accessibility_closest_origin_destinations