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Usage

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Aceso API

GravityModel

class aceso.GravityModel(decay_function, decay_params={}, huff_normalization=False, suboptimality_exponent=1.0)[source]

Bases: object

Represents an instance of a gravitational model of spatial interaction.

Different choices of decay function lead to the following models:
  • Standard gravity models
  • Two-Step Floating Catchment Area (2SFCA) models
  • Enhanced 2SFCA (E2SFCA) models
  • Three-Step FCA (3SFCA) models
  • Modified 2SFCA (M2SFCA) models
  • Kernel Density 2SFCA (KD2SFCA) models

Initialize a gravitational model of spatial accessibility.

Parameters:
  • decay_function (callable or str) –

    If str, the name of a decay function in the decay module. Some available names are ‘uniform’, ‘raised_cosine’, and ‘gaussian_decay’.

    If callable, a vectorized numpy function returning demand dropoffs by distance.

  • decay_params (mapping) – Parameter: value mapping for each argument of the specified decay function. These parameters are bound to the decay function to create a one-argument callable.
  • huff_normalization (bool) –

    Flag used to normalize demand through Huff-like interaction probabilities.

    Used in 3SFCA to curtail demand over-estimation.

  • suboptimality_exponent (float) –

    Used in M2SFCA to indicate the extent to account for network suboptimality in access. This parameter allows for the differentiation between two scenarios:

    1. Three demand locations each at a distance of 1.0 mile from the sole provider;
    2. Three demand locations each at a distance of 2.0 miles from the sole provider.

    Values greater than 1.0 for this parameter will result in accessibility scores whose weighted average is less than the overall supply.
calculate_accessibility_scores(distance_matrix, demand_array=None, supply_array=None)[source]

Calculate accessibility scores from a 2D distance matrix.

Parameters:
  • distance_matrix (np.ndarray(float)) – A matrix whose entry in row i, column j is the distance between demand point i and supply point j.
  • demand_array (np.array(float) or None) – A one-dimensional array containing demand multipliers for each demand location. The length of the array must match the number of rows in distance_matrix.
  • supply_array (np.array(float) or None) – A one-dimensional array containing supply multipliers for each supply location. The length of the array must match the number of columns in distance_matrix.
Returns:

An array of access scores at each demand location.
Return type:

array

TwoStepFCA

class aceso.TwoStepFCA(radius)[source]

Bases: aceso.gravity.GravityModel

Represents an instance of the standard Two-Step Floating Catchment Area (2SFCA) model.

Initialize a 2SFCA model with the specified radius.

Parameters:radius (float) – The radius of each floating catchment. Pairs of points further than this distance apart are deemed mutually inaccessible. Points within this radius contribute the full demand amount (with no decay).

Contributing

View aceso on GitHub for more information about how to contribute.

Indices and tables