Basemaps provide the geographic foundation for your map visualizations, containing the boundaries, regions, and locations you need to display data geographically.
Basemaps are maps stored in GeoJSON format, containing geographic features such as polygons, points, and lines, which represent locations such as countries, provinces, or cities. Once imported into a Mappica project and added to a Map element, a basemap visually displays these geographic features as a background layer, with data either overlaid on top (in the case of Bar Maps, Spike Maps, and Symbol Maps) or assigned to each basemap feature (in the case of Choropleths).
In the Project tab on the left of the screen, select New Basemap. The following options are available:
Consider using the free Mapshaper web tool to convert basemaps to GeoJSON format or reduce their size (using their Simplify option). Most basemaps can be reduced to under 500 KB, which significantly improves their loading time without appreciably reducing their quality. Find out more about how to prepare GeoJSON files here.
After you add a basemap to your project, the basemap is automatically selected and a preview is displayed. In the Basemap tab in the right panel of the screen, the following functionality is available in the Setup section:
Rotation values describe how the globe is repositioned relative to the viewer. As a result, it is conventional for positive longitude rotation to move the map's central meridian westward. For example, a longitude rotation of +90 centers the map on the 90°W (or -90°) line of longitude. Similarly, positive latitude rotation shifts the map's focus southward. For instance, a latitude rotation of +30 centers the map on the 30°S parallel (or -30°).
Graticules consist of a set of latitude and longitude lines overlaid on a map to create a coordinate grid. These lines provide a clear visual guide to geographic locations and are helpful for understanding spatial relationships between points. In Mappica, you can overlay graticules onto your basemap by selecting the Show Graticules icon in the toolbar.
With graticules enabled, you will be able to see lines of latitude and longitude at 10° intervals. In addition, color-coded graticules are displayed for the Prime Meridian, the Central Meridian, the Equator, the Central Parallel, and, when a conic projection is selected, Standard Parallels.
A feature represents a single unit of geographic data, such as a point, line, or polygon, and includes associated properties (e.g., name, population, category). Features can represent countries, provinces, cities, roads, lakes, and many other geographic entities. When you select any feature on the map, the Feature tab will display a list of properties and values for that feature. For instance, if the feature is the Canadian province of Québec, properties might include its name (Québec), administrative code (CA.10), and central latitude (52.2593) and longitude (-73.7168).
When you create a Map element in a visualization, you will need to assign it a dataset (containing the data layered onto the map) and a basemap (containing the background layer). In some instances, the dataset and basemap do not need to be connected in any way. For instance, consider a symbol map of U.S. airport traffic. Each record in the dataset used by this map corresponds with an individual airport. However, the basemap contains features for each of the 50 states, and simply acts as a background layer that is unconnected to the overlaid data.
If you are creating a Bar, Spike, or Symbol map, and wish to display one bar, spike, or symbol on each feature (i.e. on each state in the above example), you should ensure the records (rows) in the dataset match the features in the basemap, and that each dataset record contains longitude and latitude values that will appropriately position the bars, spikes, or symbols on each feature.
If you are creating a Choropleth map, dataset records must match the features in the basemap, since a choropleth assigns colors to each feature based on data values. You will need to ensure that there is one record in your dataset for every basemap feature, and you will need to join the dataset and basemap by selecting a Dataset Join Field and a Basemap Join Field that contain matching values.
Mappica has a built-in feature that lets you create datasets with records that exactly match the features of a basemap. In the left panel, click the New Dataset button, select New Dataset from Basemap, select a basemap, and then use the checkboxes to select which basemap properties to add as fields (columns) in the new dataset. The dataset will contain a record (row) for every basemap feature.
If you are using the New Dataset from Basemap feature and intend to create a choropleth map, ensure you select at least one field that contains unique values for every basemap feature. You will use this field to join the dataset and basemap. If you intend to create a bar, spike, or symbol map, select latitude and longitude (if they are available), since these can be used to position the dataset bars, spikes, or symbols appropriately.