The geographic dimension plays a fundamental role in multidimensional systems. To define a geographic dimension in a star schema, we need a table with attributes corresponding to the levels of the dimension. Additionally, we will also need one or more geographic layers to represent the data using this dimension.
We can obtain this data from available vector layers of geographic information. In simple cases, one layer is enough; but we often need several layers related to each other. The relationships can be defined by common attribute values or can be inferred from the respective geographic information.
The goal of geodimension is to support the definition of geographic
dimensions from layers of geographic information that can be used in
multidimensional systems. In particular, through package
geomultistar they
can be used directly.
You can install the released version of geodimension from
CRAN with:
install.packages("geodimension")And the development version from GitHub with:
# install.packages("devtools")
devtools::install_github("josesamos/geodimension")This is a basic example which shows you how to generate a geodimension
from several vector layers of geographic information. It also shows how
to use it.
Suppose that, for the US, we want to define a geographic dimension at
the state level but also include the information at the predefined
higher organization levels: region, division and also nation. We
have obtained geographic layers for each of these levels:
layer_us_state, layer_us_region, layer_us_division and
layer_us_nation. From each layer, we define a geolevel.
library(geodimension)
state <-
geolevel(name = "state",
layer = layer_us_state,
key = c("geoid")) |>
complete_point_geometry()
region <-
geolevel(name = "region",
layer = layer_us_region,
key = c("geoid"))
division <-
geolevel(name = "division",
layer = layer_us_division,
key = c("geoid"))
nation <-
geolevel(name = "nation",
layer = layer_us_nation,
key = c("geoid"))We define a geodimension that includes all the levels in which we are
interested.
gd <-
geodimension(name = "gd_us",
level = region) |>
add_level(division) |>
add_level(state) |>
add_level(nation)Next, we define the relationships that exist between the levels: some based on common attributes, others on geographic relationships between their instances.
gd <- gd |>
relate_levels(lower_level_name = "state",
lower_level_attributes = c("division"),
upper_level_name = "division") |>
relate_levels(lower_level_name = "division",
upper_level_name = "region",
by_geography = TRUE) |>
relate_levels(lower_level_name = "region",
upper_level_name = "nation",
by_geography = TRUE)There are no restrictions on the relationships you define, as long as the relationship can be established.
With these operations we have defined a geodimension. From it we can
obtain the data table to define a dimension in a star schema or the
layer or layers associated with that table at the level we need.
ld <- gd |>
get_level_data(level_name = "division")
names(ld)
#> [1] "division_key" "geoid" "divisionce" "affgeoid" "name"
#> [6] "lsad" "aland" "awater"
ld <- gd |>
get_level_data(level_name = "division",
inherited = TRUE)
names(ld)
#> [1] "division_key" "geoid" "divisionce"
#> [4] "affgeoid" "name" "lsad"
#> [7] "aland" "awater" "NATION_nation_key"
#> [10] "NATION_geoid" "NATION_affgeoid" "NATION_name"
#> [13] "REGION_region_key" "REGION_geoid" "REGION_regionce"
#> [16] "REGION_affgeoid" "REGION_name" "REGION_lsad"
#> [19] "REGION_aland" "REGION_awater"
ll <- gd |>
get_level_layer(level_name = "division",
inherited = TRUE)
names(ll)
#> [1] "geoid" "divisionce" "affgeoid"
#> [4] "name" "lsad" "aland"
#> [7] "awater" "NATION_nation_key" "NATION_geoid"
#> [10] "NATION_affgeoid" "NATION_name" "REGION_region_key"
#> [13] "REGION_geoid" "REGION_regionce" "REGION_affgeoid"
#> [16] "REGION_name" "REGION_lsad" "REGION_aland"
#> [19] "REGION_awater" "geom"If we need the data at another level of detail, we can obtain it in a similar way.
ld <- gd |>
get_level_data(level_name = "state",
inherited = TRUE)
names(ld)
#> [1] "state_key" "geoid" "region"
#> [4] "division" "statefp" "statens"
#> [7] "stusps" "name" "lsad"
#> [10] "mtfcc" "funcstat" "aland"
#> [13] "awater" "intptlat" "intptlon"
#> [16] "shape_length" "shape_area" "geoid_data"
#> [19] "DIVISION_division_key" "DIVISION_geoid" "DIVISION_divisionce"
#> [22] "DIVISION_affgeoid" "DIVISION_name" "DIVISION_lsad"
#> [25] "DIVISION_aland" "DIVISION_awater" "NATION_nation_key"
#> [28] "NATION_geoid" "NATION_affgeoid" "NATION_name"
#> [31] "REGION_region_key" "REGION_geoid" "REGION_regionce"
#> [34] "REGION_affgeoid" "REGION_name" "REGION_lsad"
#> [37] "REGION_aland" "REGION_awater"
ll <- gd |>
get_level_layer(level_name = "state",
only_key = TRUE)
plot(ll)
In addition to these functions, the package offers other support
functions to aid in the definition of levels (for example, to determine
the key attributes of a layer), to relate instances of levels whose
relationship is not immediately established, or to configure the
geodimension to obtain a customized output.
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