Arc map
Updated 2 years ago to v6.0.1 by Flourish team
How to use this template
What's it for?
Use this template to visualise flows between locations, or journeys.
How to get started
You'll need two CSV or Excel files. One will contain the locations of the points shown on your map - the start and end points of your arcs. The other will contain the details of the arcs themselves.
The locations file will need (at a minimum) columns for the location identifier, latitude and longitude. Here's an example:
airport_id latitude longitude 1 -6.081689835 145.3919983 2 -5.207079887 145.7890015 3 -5.826789856 144.2960052 The arcs file will need (at a minimum) columns for the source ID and target ID of the arc. You can also include columns that can be used to specify the colour or thickness of the arc. Here's an example:
source_id target_id airline 1 2 American Airlines 2 3 American Airlines 1 3 United Airlines
Not sure how to upload your data to Flourish? See our handy guide
FAQ
How do I reset the initial zoom and centre of the map? For the moment, you need to do this: (1) Create a story from your visualisation (2) Zoom and pan the slide to adjust the zoom and centre of the map (3) In the left-hand menu, under "Navigation", choose "None" (4) Publish the story.
How do I change the colour of the arcs? Two methods. If you'd like them all to be the same colour, use the settings in the settings panel. If you'd like the colours to vary with some property of the data, select a "Category" column in the data panel. Then return to the settings panel and choose the Categorical colour option.
How do I change the thickness of the arcs? Two methods. If you'd like to make all the arcs thicker or thinner, just use the "Thickness" setting to do so. If you'd like the thickness to vary with some property of the data, select a "Value" column in the data panel. Then return to the settings panel and choose the Categorical colour option.
How can I highlight different points on the map? Create a story from your visualisation, then add multiple slides to highlight different views of the data. See the example story below.
Examples
Credits
Created by the Flourish team, using deck.gl and Mapbox GL JS. Want to see additional features? Let us know at support@flourish.studio.
API information
This section documents API usage specific to this template, so for an introduction we suggest you refer to the generic API documentation instead.
template: @flourish/3d-arc-map
version: 6
Template data
There are three different formats in which you can supply data to this template. The most convenient for you to use likely depends on the source of your data, as described below.
1. Array of arrays, and a bindings object
You can supply arrays of arrays to opts.data
, which might look
like:
{ data: { routes: [ [ "RoutesColumn1Value1", "RoutesColumn2Value1", [ "RoutesColumn1Value2", "RoutesColumn2Value2", [ "RoutesColumn1Value3", "RoutesColumn2Value3", ... ], locations: [ [ "LocationsColumn1Value1", "LocationsColumn2Value1", [ "LocationsColumn1Value2", "LocationsColumn2Value2", [ "LocationsColumn1Value3", "LocationsColumn2Value3", ... ], regions: [ [ "RegionsColumn1Value1", "RegionsColumn2Value1", [ "RegionsColumn1Value2", "RegionsColumn2Value2", [ "RegionsColumn1Value3", "RegionsColumn2Value3", ... ] } }
where each array of arrays represents the rows in a data sheet.
To tell the API how the values from each column should be
associated with the keys that the template is expecting, you must also supply
an object attached to opts.bindings
. (The meanings of the
keys in the bindings object are documented
below.) The minimal bindings you can
supply for this template are as shown in this example:
{ template: "@flourish/3d-arc-map", version: "6", bindings: { routes: { source: 0, // index of a column in your data target: 1, // index of a column in your data }, locations: { id: 0, // index of a column in your data latitude: 1, // index of a column in your data longitude: 2, // index of a column in your data }, regions: { } }, data: { routes: [ [ "RoutesColumn1Value1", "RoutesColumn2Value1", [ "RoutesColumn1Value2", "RoutesColumn2Value2", [ "RoutesColumn1Value3", "RoutesColumn2Value3", ... ], locations: [ [ "LocationsColumn1Value1", "LocationsColumn2Value1", [ "LocationsColumn1Value2", "LocationsColumn2Value2", [ "LocationsColumn1Value3", "LocationsColumn2Value3", ... ], regions: [ [ "RegionsColumn1Value1", "RegionsColumn2Value1", [ "RegionsColumn1Value2", "RegionsColumn2Value2", [ "RegionsColumn1Value3", "RegionsColumn2Value3", ... ] } }
All possible bindings that you can supply are shown in this example:
{ template: "@flourish/3d-arc-map", version: "6", bindings: { routes: { source: 0, // index of a column in your data target: 1, // index of a column in your data width: 2, // index of a column in your data filter: 3, // index of a column in your data category: 4, // index of a column in your data metadata: [5, 6, ...], // index(es) of column(s) in your data }, locations: { id: 0, // index of a column in your data latitude: 1, // index of a column in your data longitude: 2, // index of a column in your data name: 3, // index of a column in your data category: 4, // index of a column in your data }, regions: { geojson: 0, // index of a column in your data } }, data: { routes: [ [ "RoutesColumn1Value1", "RoutesColumn2Value1", [ "RoutesColumn1Value2", "RoutesColumn2Value2", [ "RoutesColumn1Value3", "RoutesColumn2Value3", ... ], locations: [ [ "LocationsColumn1Value1", "LocationsColumn2Value1", [ "LocationsColumn1Value2", "LocationsColumn2Value2", [ "LocationsColumn1Value3", "LocationsColumn2Value3", ... ], regions: [ [ "RegionsColumn1Value1", "RegionsColumn2Value1", [ "RegionsColumn1Value2", "RegionsColumn2Value2", [ "RegionsColumn1Value3", "RegionsColumn2Value3", ... ] } }
2. Array of objects with arbitrary keys, and a bindings object
This format is most likely useful when you have data from an external source,
such as CSV data loaded from d3-dsv.
You should supply this attached to the opts.data
, which might look
like:
{ routes: [ { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, ... ], locations: [ { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, ... ], regions: [ { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, ... ] }
... but with the keys being the column headers from your
source data instead. You must also supply an object attached to
opts.bindings
. The minimal bindings you can
supply for this template are as shown in this example:
{ template: "@flourish/3d-arc-map", version: "6", bindings: { routes: { source: "RoutesHeader1", target: "RoutesHeader2", }, locations: { id: "LocationsHeader1", latitude: "LocationsHeader2", longitude: "LocationsHeader3", }, regions: { } }, data: { routes: [ { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, ... ], locations: [ { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, ... ], regions: [ { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, ... ] } }
All possible bindings that you can supply are shown in this example:
{ template: "@flourish/3d-arc-map", version: "6", bindings: { routes: { source: "RoutesHeader1", target: "RoutesHeader2", width: "RoutesHeader3", filter: "RoutesHeader4", category: "RoutesHeader5", metadata: ["RoutesHeader6", "RoutesHeader7", ...], }, locations: { id: "LocationsHeader1", latitude: "LocationsHeader2", longitude: "LocationsHeader3", name: "LocationsHeader4", category: "LocationsHeader5", }, regions: { geojson: "RegionsHeader1", } }, data: { routes: [ { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, { "RoutesHeader1": ..., "RoutesHeader2": ..., ... }, ... ], locations: [ { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, { "LocationsHeader1": ..., "LocationsHeader2": ..., ... }, ... ], regions: [ { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, { "RegionsHeader1": ..., "RegionsHeader2": ..., ... }, ... ] } }
(As before, the keys containing "Header" would be replaced by column names from your data source.)
3. Array of objects with template-defined keys
There is an alternative format you can use, which is likely to be easier to
use if your data is not from a spreadsheet source. With this alternative format
you supply your data to the template as
an array of objects, attached to opts.data
, where the keys must
be those used by the template, as documented below. In this case
there is no need to supply a bindings object, since the key names are already
those expected by the template. The required properties in the data
object are as follows (scroll down for a
description of what each property is):
{ template: "@flourish/3d-arc-map", version: "6", data: { routes: [ { source: ..., target: ..., metadata: [...] }, ... ], locations: [ { id: ..., latitude: ..., longitude: ... }, ... ] }, ... }
And the full list of all possible properties is as follows:
{ template: "@flourish/3d-arc-map", version: "6", data: { routes: [ { source: ..., target: ..., width: ..., filter: ..., category: ..., metadata: [...] }, ... ], locations: [ { id: ..., latitude: ..., longitude: ..., name: ..., category: ... }, ... ], regions: [ { geojson: ... }, ... ] }, ... }
Meanings of the template data keys:
- routes.source: The column containing the code for the arc's source. This should match the codes used in the Locations sheet
- routes.target: The column containing the code for the arc's target, This should match the codes used in the Locations sheet
- routes.width: Optionally, a column containing a value for the arc, which can be used to specify its thickness.
- routes.filter: Optionally, a column to filter visible arcs by.
- routes.category: Optionally, a column containing a category for the arc, which can be used to specify its colour. Over-rides the category in the Locations sheet, if both are specified.
- routes.metadata: metadata
- locations.id: The column containing the location code. Should match the codes used in the Arcs sheet.
- locations.latitude: latitude
- locations.longitude: longitude
- locations.name: Optionally, a column containing the name of the location, to show in popup
- locations.category: Optionally, a column containing the category of the arc, which can be used to specify its colour.
- regions.geojson: geojson
Template settings
Options for opts.state
.
Arcs
arc.arc_thickness number
Thickness.
arc.brushing_enabled boolean
Brushing enabled.
arc.brushing_brush_source boolean
Brush source.
arc.brushing_brush_target boolean
Brush target.
arc.brushing_brush_radius number
Brush radius (meters).
arc.arc_palette_enabled boolean
Type. Allowed values:
arc.arc_source_color color
Source color.
arc.arc_source_opacity number
Source opacity. Max: 1
arc.arc_target_color color
Target color.
arc.arc_target_opacity number
Target opacity. Max: 1
arc.arc_palette.scale_type string
Scale type. Allowed values:
arc.arc_palette.categorical_type string
Allowed values:
- palette (Palette)
- generated (Generated)
arc.arc_palette.categorical_palette colors
Palette.
arc.arc_palette.categorical_extend boolean
Auto-extend. Automatically generate additional colours when needed to avoid the palette colours being used more than once.
arc.arc_palette.categorical_seed_color color
Seed color. Initial color in generated sequence (avoid shades of grey).
arc.arc_palette.categorical_rotation_angle number
Hue rotation angle. Angle, in degrees, between one generated colour and the next. The default value, ~360/(Golden ratio), ensures adjacent hues are not too similar. Max: 360
arc.arc_palette.categorical_color_space string
Allowed values:
- hcl (HCL)
- hsl (HSL)
arc.arc_palette.categorical_custom_palette text
Custom overrides. Type the name of the entity whose colour you want to set, a colon and then a colour (using a name, hex-code or rgb declaration). Multiple colours can be set using multiple lines. For example:
Party 1: red
Party 2: #4455AA
Party 3: rgb(30,168,26)
arc.arc_palette.sequential_palette string
Palette. Allowed values:
arc.arc_palette.sequential_custom_min color
Minimum color.
arc.arc_palette.sequential_custom_max color
Maximum color.
arc.arc_palette.sequential_color_space string
Allowed values:
- rgb (RGB)
- lab (LAB)
- hcl (HCL)
- hsl (HSL)
arc.arc_palette.sequential_reverse boolean
Reverse scale.
arc.arc_palette.diverging_palette string
Palette. Allowed values:
arc.arc_palette.diverging_custom_min color
Minimum color.
arc.arc_palette.diverging_custom_mid color
Midpoint color.
arc.arc_palette.diverging_custom_max color
Maximum color.
arc.arc_palette.diverging_color_space string
Allowed values:
- rgb (RGB)
- lab (LAB)
- hcl (HCL)
- hsl (HSL)
arc.arc_palette.diverging_reverse boolean
Reverse scale.
Map
map.style_enabled boolean
Allowed values:
- true (Enable)
- false (Disable)
map.style_base string
Map style. Allowed values:
map.style_monochrome_color color
Map base color.
map.style_show_borders boolean
Display borders.
map.style_show_roads boolean
Display transport.
map.style_show_labels boolean
Display labels.
map.style_show_landuse boolean
Display land use.
map.style_show_water boolean
Display water.
map.map_language_auto boolean
Detect language. Automatically changes the language used on the base map to match the viewer's language settings.
map.map_language_alts boolean
Display alternatives. Whether or not to display latin alternatives for non-latin languages (or vice versa)
map.map_language string
Language. Allowed values:
map.map_zoom_min number
Min zoom. Max: 22
map.map_zoom_max number
Max zoom. Max: 22
map.map_bound_position boolean
Limit viewport bounds.
map.map_lat_min number
Min latitude. Min: -90 Max: 90
map.map_lat_max number
Max latitude. Min: -90 Max: 90
map.map_lng_min number
Min longitude. Min: -180 Max: 180
map.map_lng_max number
Max longitude. Min: -180 Max: 180
map.map_initial_type string
Initial viewport. By default, the initial viewport of the map is automatically set to include every visible object. The "centroid" option allows you to select a custom latitude, longitude and zoom. The "bounds" option lets you specify a custom bounding box for the viewport to enclose. Allowed values:
map.map_initial_pitch number
Pitch. Max: 60
map.map_initial_bearing number
Bearing. Min: -180 Max: 180
map.map_initial_lat number
Latitude. Min: -90 Max: 90
map.map_initial_lng number
Longitude. Min: -180 Max: 180
map.map_initial_zoom number
Zoom. Max: 22
map.map_initial_bounds_lat_min number
Min latitude. Min: -90 Max: 90
map.map_initial_bounds_lng_min number
Min longitude. Min: -180 Max: 180
map.map_initial_bounds_lat_max number
Max latitude. Min: -90 Max: 90
map.map_initial_bounds_lng_max number
Max longitude. Min: -180 Max: 180
map.map_interactive boolean
Allow user interaction.
map.map_hijack_scroll boolean
Require cmd/ctrl to zoom when scrolling.
map.controls_geolocator_enabled boolean
Use geolocator control.
map.controls_geolocator_alignment string
Geolocator control position. Allowed values:
map.controls_fullscreen_enabled boolean
Use fullscreen control.
map.controls_fullscreen_alignment string
Fullscreen control position. Allowed values:
map.animation_enabled boolean
Enable animation.
map.animation_duration number
Duration. Max: 4
Inset map
minimap.minimap_display boolean
Display map.
minimap.minimap_rotate boolean
Rotate with camera.
minimap.minimap_custom_colors boolean
Customise colours.
minimap.minimap_fill color
Region fill color.
minimap.minimap_ocean_color color
Ocean color.
minimap.minimap_stroke color
Region stroke color.
minimap.minimap_outline color
Outline color.
minimap.minimap_show_bounds boolean
Display viewport bounds.
minimap.minimap_bounds_color color
Region bounds color.
minimap.minimap_bounds_opacity number
Region bounds opacity. Max: 1
minimap.minimap_size_type string
Size units. Allowed values:
minimap.minimap_size_desktop_pixels number
Pixels (desktop). Min: 1
minimap.minimap_size_mobile_pixels number
Pixels (mobile). Min: 1
minimap.minimap_size_desktop_viewport number
Screen % (desktop). Min: 1 Max: 100
minimap.minimap_size_mobile_viewport number
Screen % (mobile). Min: 1 Max: 100
Filtering
filter_controls.type string
Data type. Allowed values:
filter_controls.temporal_format string
Date/time format in data. The date/time format in your data sheet. Used only to sort the data, if required. If your format isn’t in the list, you can enter a custom format using d3-time-format syntax. See npmjs.com/package/d3-time-format for details. Predefined values:
filter_controls.sort boolean
Sort menu.
filter_controls.control string
Control. Allowed values:
filter_controls.width number
Menu width. Min: 150
filter_controls.play_button boolean
Include play button.
filter_controls.step_time number
Time between steps when playing. Measured in seconds, positive values move the slider left to right, negative values move the slider right to left.
filter_controls.loop boolean
Loop on play.
filter_controls.restart_pause number
Pause before loop restarts. Measured in seconds and in addition to the regular step time displayed above.
filter_controls.dropdown_icon_color color
Icon color.
filter_controls.slider_handle_color color
Handle and button color.
filter_controls.slider_track_color color
Track and label color.
Popup
popup.show_popups boolean
Popups. Allowed values:
popup.is_custom boolean
Popup contents. Allowed values:
popup.custom_template text
Popup content. The text to appear in the popup. You can use {{column_name}} to add a value from your data. It must be in a selected column, but you can add columns to “Metadata” if you just want to include them for use in the popup. Advanced users can include HTML to apply layouts, formatting, images, etc.
popup.show_pointer boolean
Pointer.
popup.show_shadow boolean
Shadow.
popup.style_popups boolean
Custom styling.
popup.text_color color
Text colour.
popup.align string
Alignment. Allowed values:
popup.font_size number
Font size. Min: 1
popup.fill_color color
Fill colour.
popup.opacity number
Fill opacity. Max: 1
popup.padding number
Padding.
popup.border_radius number
Radius. Corner radius of popup
Layout
Layout
layout.body_font font
Main font. This font will apply to the whole graphic by default, but you can optionally change the font for the title, subtitle, footer, etc in the Header and Footer settings panels.
layout.font_color color
Text color. This color will apply to the whole graphic by default, but you can optionally change the color for individual text elements, in other settings panels.
layout.background_color_enabled boolean
Color. Allowed values:
layout.background_image_enabled boolean
Image. Allowed values:
layout.background_color color
Background color.
layout.background_image_src url
Image URL.
layout.background_image_size string
Size. Allowed values:
layout.background_image_position string
Position. Allowed values:
layout.max_width_target string
Maximum width. Apply a maximum width to just the main graphic or everything (main graphic plus header, footer, etc) Allowed values:
layout.max_width number
Maximum width. Leave blank to stretch to container width Min: 50
layout.max_width_align string
Align. Allowed values:
layout.layout_order string
Layout order. Allowed values:
layout.space_between_sections string
Space between sections. Allowed values:
layout.space_between_sections_custom number
Custom. Max: 100
layout.margin_top number
Top.
layout.margin_right number
Right.
layout.margin_bottom number
Bottom.
layout.margin_left number
Left.
layout.border.enabled boolean
Show borders around visualisation.
layout.border.top.width number
Top.
layout.border.top.style string
Style. Allowed values:
layout.border.top.color color
Color.
layout.border.right.width number
Right.
layout.border.right.style string
Style. Allowed values:
layout.border.right.color color
Color.
layout.border.bottom.width number
Bottom.
layout.border.bottom.style string
Style. Allowed values:
layout.border.bottom.color color
Color.
layout.border.left.width number
Left.
layout.border.left.style string
Style. Allowed values:
layout.border.left.color color
Color.
layout.read_direction string
Read direction. This will change the reading direction of the main text elements on the page. Its not possible to adjust this on all elements such as axes. Note that when direction is set to "right to left" any alignment icons will be reversed. Allowed values:
Header
layout.header_align string
Alignment. Allowed values:
layout.title html
layout.title_styling boolean
Styling.
layout.title_font font
Title Font.
layout.title_size string
Size. Allowed values:
layout.title_size_custom number
Custom. Specify a custom responsive font size. Best results will be with values between 1.2 and 3
layout.title_weight string
Weight. Allowed values:
layout.title_color color
Color.
layout.title_line_height number
Line height. Max: 3
layout.title_space_above string
Space above. Allowed values:
layout.title_space_above_custom number
Custom. Max: 100
layout.subtitle html
layout.subtitle_styling boolean
Styling.
layout.subtitle_font font
Subtitle Font.
layout.subtitle_size string
Size. Allowed values:
layout.subtitle_size_custom number
Custom. Specify a custom responsive font size. Best results will be with values between 1.2 and 3
layout.subtitle_weight string
Weight. Allowed values:
layout.subtitle_color color
Color.
layout.subtitle_line_height number
Line height. Max: 3
layout.subtitle_space_above string
Space above. Allowed values:
layout.subtitle_space_above_custom number
Custom. Max: 100
layout.header_text html
layout.header_text_styling boolean
Styling.
layout.header_text_size string
Size. Allowed values:
layout.header_text_size_custom number
Custom. Specify a custom responsive font size. Best results will be with values between 1.2 and 3
layout.header_text_weight string
Weight. Allowed values:
layout.header_text_color color
Color.
layout.header_text_line_height number
Line height. Max: 3
layout.header_text_space_above string
Space above. Allowed values:
layout.header_text_space_above_custom number
Custom. Max: 100
layout.header_border string
Allowed values:
- top (Top)
- bottom (Bottom)
- top_and_bottom (Top & bottom)
- none (None)
layout.header_border_width number
Width.
layout.header_border_color color
Color.
layout.header_border_style string
Style. Allowed values:
layout.header_border_space number
Space. Space between border and header text
layout.header_logo_enabled boolean
Allowed values:
- true (Enabled)
- false (Disabled)
layout.header_logo_src url
Image.
layout.header_logo_link_url string
Link.
layout.header_logo_height number
Height.
layout.header_logo_align string
Align. Align logo inside either the header or the main visualisation container Allowed values:
layout.header_logo_position_inside string
Position. Allowed values:
layout.header_logo_position_outside string
Position. Allowed values:
layout.header_logo_margin_top number
Top.
layout.header_logo_margin_right number
Right.
layout.header_logo_margin_bottom number
Bottom.
layout.header_logo_margin_left number
Left.
Footer
layout.footer_align string
Alignment. Allowed values:
layout.footer_text_size number
Size.
layout.footer_text_color color
Color.
layout.footer_styling boolean
Advanced footer styles.
layout.footer_font font
Font.
layout.footer_text_weight string
Weight. Allowed values:
layout.source_name string
Source name.
layout.source_url string
Source url.
layout.multiple_sources boolean
Multiple sources.
layout.source_name_2 string
Source name.
layout.source_url_2 string
Source url.
layout.source_name_3 string
Source name.
layout.source_url_3 string
Source url.
layout.source_label string
Source label.
layout.footer_note string
Note.
layout.footer_note_secondary string
Note (secondary). The secondary note is placed below the source and primary note
layout.footer_logo_enabled boolean
Image. Allowed values:
layout.footer_logo_src url
Image.
layout.footer_logo_src_light hidden
Image (light version). If provided this version will be used whenever the background colour is dark
layout.footer_logo_link_url string
Link.
layout.footer_logo_height number
Height.
layout.footer_logo_margin number
Margin.
layout.footer_logo_order string
Position. Allowed values:
layout.footer_align_vertical string
V. align. Allowed values:
layout.footer_border string
Allowed values:
- top (Top)
- bottom (Bottom)
- top_and_bottom (Top & bottom)
- none (None)
layout.footer_border_width number
Width.
layout.footer_border_color color
Color.
layout.footer_border_style string
Style. Allowed values:
layout.footer_border_space number
Space. Space between border and footer text
Accessibility
layout.screenreader_hide_primary boolean
Screenreader mode for main visual container. Whether the main visual container is visible to screenreaders. (Text in the header and footer are always available to screenreaders.) Allowed values:
layout.screenreader_text_primary text
Screenreader description. A text alternative to the visual content that will only be visible to screenreaders, e.g. “The line chart shows China consistently higher than the other countries since 1990”. Do not replicate your title, since that will also be read by screenreaders.
layout.screenreader_label string
Screenreader label. A short text label given to the main Flourish embed wrapper to provide an accessible name that is only visible to screenreaders. Added in the form of an "aria-label".