KoboToolbox allows the collection of spatial data
through three questions types: geopoint,
geotrace and geoshape.
Geopoint:
The geopoint question type captures a
single geographic coordinate (latitude and longitude) including altitude
and accuracy. This is useful for marking locations, such as homes,
schools, or water sources.
Geotrace:
The geotrace question type collects a
series of connected geographic coordinates, forming a line. This can be
used to map routes, paths, or boundaries.
Geoshape:
A geoshape question type captures a
series of geographic coordinates that form a closed polygon. This is
useful for defining areas, such as land parcels, agricultural fields, or
protected zones.
To utilize these data types, we need to parse them into a GIS
friendly format. robotoolbox uses Well-Known Text
(WKT), a standard markup language for representing vector geometry,
to represent points (geopoint), lines
(geotrace) and polygons (geoshape).
Spatial data
The following form provides a simple demonstration of how
robotoolbox maps spatial field types.
Survey questions
| name | type | label |
|---|---|---|
| point | geopoint | Record a location |
| point_description | text | Describe the recorded location |
| line | geotrace | Record a line |
| line_description | text | Describe the recorded line |
| polygon | geoshape | Record a polygon |
| polygon_description | text | Describe the recorded polygon |
The form includes three spatial type columns: point,
line and polygon.
Loading the project
The aforementioned form, named Spatial data, was
uploaded to the server. You can load it from the asset_list
of assets.
library(robotoolbox)
library(dplyr)
asset_list <- kobo_asset_list()
uid <- filter(asset_list, name == "Spatial data") |>
pull(uid)
asset <- kobo_asset(uid)
asset#> <robotoolbox asset> a9NCKTJxBPKdy49gX57WL5
#> Asset name: Spatial data
#> Asset type: survey
#> Asset owner: dickoa
#> Created: 2023-04-22 11:57:54
#> Last modified: 2023-04-22 12:01:39
#> Submissions: 1We have a single submission, where we recorded one location using a
geopoint question, mapped a portion of a road using a
geotrace question, and outlined a stadium using a
`geoshape`` question.
Extracting the data
From the assets, we can proceed to extract the submissions.
#> Rows: 1
#> Columns: 23
#> $ point <chr> "14.719783 -17.459261 0 0"
#> $ point_latitude <dbl> 14.71978
#> $ point_longitude <dbl> -17.45926
#> $ point_altitude <dbl> 0
#> $ point_precision <dbl> 0
#> $ point_wkt <chr> "POINT (-17.459261 14.719783 0)"
#> $ point_description <chr> "Jardin Liberte"
#> $ line <chr> "14.726129 -17.500409 0 0;14.726253 -17.498993 0 …
#> $ line_wkt <chr> "LINESTRING (-17.500409 14.726129 0, -17.498993 1…
#> $ line_description <chr> "Route de la Corniche"
#> $ polygon <chr> "14.747328 -17.452461 0 0;14.747743 -17.451869 0 …
#> $ polygon_wkt <chr> "POLYGON ((-17.452461 14.747328 0, -17.451869 14.…
#> $ polygon_description <chr> "Stade Leopold Sedar Senghor"
#> $ `_id` <int> 28557821
#> $ uuid <chr> "01c7d7250bd84ac9b604199ca98daa84"
#> $ `__version__` <chr> "v7nQkzvEV64YLAfEQv5prV"
#> $ instanceID <chr> "uuid:26c66ec5-935a-4220-8902-6de928330122"
#> $ `_xform_id_string` <chr> "a9NCKTJxBPKdy49gX57WL5"
#> $ `_uuid` <chr> "26c66ec5-935a-4220-8902-6de928330122"
#> $ `_status` <chr> "submitted_via_web"
#> $ `_submission_time` <dttm> 2023-04-22 12:07:29
#> $ `_validation_status` <chr> NA
#> $ `_submitted_by` <lgl> NAWe can see that we have all of our three columns point,
line and polygon. For each of them, we have a
corresponding WKT column.
pull(df, point)
#> [1] "14.719783 -17.459261 0 0"
#> attr(,"label")
#> [1] "Record a location"
pull(df, point_wkt)
#> [1] "POINT (-17.459261 14.719783 0)"
#> attr(,"label")
#> [1] "point_wkt"For geopoint types, robotoolbox also offers
columns for latitude, longitude, altitude, and precision.
df |>
select(starts_with("point_"))
#> # A tibble: 1 × 6
#> point_latitude point_longitude point_altitude point_precision point_wkt
#> <dbl> <dbl> <dbl> <dbl> <chr>
#> 1 14.7 -17.5 0 0 POINT (-17.4592…
#> # ℹ 1 more variable: point_description <chr>The line column, derived from the geotrace
question, has a corresponding line_wkt column.
pull(df, line)
#> [1] "14.726129 -17.500409 0 0;14.726253 -17.498993 0 0;14.725688 -17.498002 0 0;14.72527 -17.497068 0 0;14.724897 -17.496113 0 0;14.72438 -17.495383 0 0;14.723737 -17.494784 0 0"
#> attr(,"label")
#> [1] "Record a line"
pull(df, line_wkt)
#> [1] "LINESTRING (-17.500409 14.726129 0, -17.498993 14.726253 0, -17.498002 14.725688 0, -17.497068 14.72527 0, -17.496113 14.724897 0, -17.495383 14.72438 0, -17.494784 14.723737 0)"
#> attr(,"label")
#> [1] "line_wkt"Lastly, polygon_wkt is the WKT column derived from the
geoshape question labeled polygon.
pull(df, polygon)
#> [1] "14.747328 -17.452461 0 0;14.747743 -17.451869 0 0;14.747519 -17.451477 0 0;14.747244 -17.451332 0 0;14.746378 -17.451332 0 0;14.745989 -17.451563 0 0;14.745844 -17.451987 0 0;14.746062 -17.45232 0 0;14.74627 -17.452492 0 0;14.747328 -17.452461 0 0"
#> attr(,"label")
#> [1] "Record a polygon"
pull(df, polygon_wkt)
#> [1] "POLYGON ((-17.452461 14.747328 0, -17.451869 14.747743 0, -17.451477 14.747519 0, -17.451332 14.747244 0, -17.451332 14.746378 0, -17.451563 14.745989 0, -17.451987 14.745844 0, -17.45232 14.746062 0, -17.452492 14.74627 0, -17.452461 14.747328 0))"
#> attr(,"label")
#> [1] "polygon_wkt"Now that we understand how robotoolbox stores spatial
question types, we can convert these columns into spatial objects
suitable for spatial data analysis.
Geopoint
The standard approach to manipulate spatial vector data in
R involves using the sf package.
sf stands for Simple Features and it extends a
data.frame by adding a geometry list-column. It’s a
spatially enabled data.frame. It provides an interface to
the popular GDAL, GEOS, PRØJ and S2 libraries. It can be used to
efficiently manipulate and visualize spatial vector data.
Creating an sf object from a text column that contains
WKT
characters is straightforward. The sf::st_as_sf function
can be used to turn the data.frame with a WKT
column into an sf object.
point_sf <- st_as_sf(data_spatial,
wkt = "point_wkt", crs = 4326)
mapview(point_sf)Geotrace
We can also transform a data.frame with a column from a
geotrace question to an sf object with a
LINESTRING geometry. The WKT column is named
line_wkt.
line_sf <- st_as_sf(data_spatial,
wkt = "line_wkt", crs = 4326)
mapview(line_sf)Geoshape
The column polygon_wkt can be used to create an
sf polygon object. It’s a simple closed polygon.
poly_sf <- st_as_sf(data_spatial,
wkt = "polygon_wkt", crs = 4326)
mapview(poly_sf)Not only does robotoolbox rely on the sf
package, but it also leverages other packages from the same ecosystem to
provide robust spatial data analysis for KoboToolbox
users.
You can learn a lot about the sf packages and spatial
data analysis with R from the excellent Geocomputation with R book and
through the extensive sf package documentation.