Map view in JOSM

This is the main view in JOSM (also called ​Viewport), where editing takes place, and Bing/Mapbox and other sources can be displayed.

What do you see here and when

There are several mechanisms in JOSM that affect what the user sees in the map view.

Visibility

• Data can be filtered out by Filters
• Layers (data, imagery)
  • can be hidden or can be set to semi-opaque
  • can be obscured by other data layers (Up/Down buttons are used to arrange layers)
• Map Paint Styles can hide OSM objects per zoom level

Appearance

• Partial fill of objects is enabled by default, it depends on area of the object. Areas will be fully filled if the partial fill would cover more than 50% of the area to avoid small unfilled gaps in the middle of an area.
• Enabled (in preferences) and activated (in Map Paint Styles panel or preferences) styles affect what you see on the screen
• Styles can be displayed differently based on zoom factor

Map view controls

Move map

The area can be moved by holding down the right mouse button, and dragging the mouse. To improve dragging performance, labels are hidden while moving the map:

This can be disabled in the OSM Data settings.

Zoom

• Using the scroll wheel
• + and - keys
• more specialized move/zoom actions and tools like:
  • several items in the View menu
  • Jump To Position
  • Zoom tool
  • Minimap

Downloaded area

The area which was not downloaded is indicated by a yellow hatching. Ways which were downloaded can reach into the hatched area though. Make sure to edit only in the non hatched area because else it may lead to conflicts or duplicate data after upload.

Note that if you download filtered data (e.g. only buildings via Overpass API) there will be no hatched area at all as this is an incomplete data set. As soon as you download an additional area (containing all data in this area) into this layer the hatching will appear.

In special editing scenarios it may be useful to disable the hatching. This can be done via the View menu (expert mode only) or in the OSM Data settings. Use this with caution. Only disable the hatching if you know what you are doing.

Grid

A configurable grid can be drawn over the map view, above all layers, as a visual aid: for example to see at a glance which parts of a large area have already been edited, or to lay out a regular street pattern. The grid is purely visual. There is no snapping to grid lines; drawing and editing behave exactly as without the grid.

Show and hide

View > Grid > Show. The action can also be placed on the toolbar.

Settings

View > Grid > Grid preferences... opens Preferences > Grid directly: grid type (projected coordinates in metres, or latitude/longitude in degrees), east and north spacing, rotation, origin, line width, blend mode and the minimum distance of the lines on screen. The line colors are in Preferences > Colors ("grid east lines", "grid north lines").

The default is a grid of 1000 m × 1000 m in projected coordinates, drawn in yellow with the "hard light" blend mode so that it stays visible over light and dark map features. Spacings of a projected grid are true distances in metres, the same as measured by the parallel way tool and the status bar. When zooming out, the spacing is automatically multiplied by 10 (100, 1000, ...) as soon as the lines would come closer than a configurable number of pixels, so the grid stays readable while remaining aligned to the configured one.

Latitude/longitude grid and the world bounds: when zoomed out far enough that the edge of the projection's usable area (e.g. ±85° latitude for the default Mercator projection) becomes visible, the meridians stop at that edge instead of continuing to the pole. This is correct: it is the same limit the projection itself, the downloaded data and the background imagery are subject to, not a defect of the grid.

Placing the grid from the current selection

Two entries of View > Grid position the grid from the current selection in the data layer, without typing coordinates:

Set origin to selection

Moves the grid so that a north-south and an east-west line cross at the selected point, and switches the grid on. Select a single node (for example a street intersection) to use its exact position; with any other selection (several nodes, one or more ways, a relation) the origin is the centroid — the arithmetic mean position of every node reachable from the selection. For a projected grid the origin is also the point at which the metric spacing is exact, so pick a point inside the area you work in. The entry is disabled while the selection contains no node with known coordinates.

Align rotation to selection

Rotates the grid so that its lines run parallel to the current selection: either a single way (direction from its first to its last node) or exactly two nodes. Select a long, straight stretch of one of the streets first. The grid is switched to projected coordinates (a latitude/longitude grid cannot be rotated) and switched on. The entry is disabled while the selection does not define a direction.

Both entries follow the selection live, so they enable and disable themselves as you select and deselect objects; there is no need to reopen the menu.

Typical workflow for an existing regular street grid: select a straight main street, View > Grid > Align rotation to selection; then select the node at a street intersection, View > Grid > Set origin to selection; finally set the block size as spacing via View > Grid > Grid preferences....

Tile borders of imagery layers

Independent of the grid, imagery layers can draw a thin border around each of their tiles: right click on the map (or on the layer in the layer list) and check Show tile borders. This helps to tell which tile is being looked at, for example together with Show tile info. The setting applies to that layer and is stored with it in sessions; switching it on or off is also remembered, so layers opened later and after a restart of JOSM follow the last choice. Its color is "imagery tile border" in Preferences > Colors.

Troubleshooting

On a Mac with a one-button mouse, simulate right-click by holding down Ctrl while clicking the button.

See also

• Select Action - help on selecting, moving, and rotating objects in the map view
• Modes - overview of modes (frequently accessed tools) in JOSM
• Status bar
• Imagery Context Menu

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