'Convert configured parameters to keyword args for __init__().'

@staticmethod
def prepareKeywordArgs(config_dict):

    kwargs = {'mapfile': config_dict['mapfile']}
    for key in ('fields', 'layers', 'layer_index', 'scale', 'layer_id_key'):
        if (key in config_dict):
            kwargs[key] = config_dict[key]
    return kwargs
