A
base map is a map which shows the existing physical pattern of the land upon
which survey info analysis or planning proposal can be superimposed. The
information required for base map varies from map to map because it largely
depends upon its scale, the area covered and the level of planning details. The
base map, with its corresponding representation of the topography of the
territory, shows the physical reality of the area where the new city plan is to
be implemented. This physical reality is expressed through cartography, an
absolutely essential component and probably the most important of all those
comprising the information necessary for carrying out urban planning.
A
base map is the graphic representation at a specified scale of selected
fundamental map information; used as a framework upon which additional data of
a specialized nature may be compiled. Within the multipurpose cadastre, the
base map provides a primary medium by which the locations of cadastral parcels
can be related to the geodetic reference framework; to major natural and
man-made features such as bodies of water. roads, buildings, and fences; and to
municipal and political boundaries. The base map also provides the means by
which all land related information may be related graphically to cadastral
parcels.
Base Map Features:
Before
taking up any urban development plan exercise the first task, both from
planning point of view and as statutory requirement, is to prepare or obtain
reliable, accurate and up‐to‐date base map for the respective town or city for
which the plan is being prepared. The amount of information to be represented
on the map varies from map to map because information depiction depends
on:
·
Purpose
of map
·
Scale
·
Projection
·
Method
of map‐making
·
Draughting
skill
Uniformity of base map with regard to presentation of features, scale, size and notations, facilitates the readability of these maps and comparison of one map with another. Mapping software of Remote Sensing and Geographical Information System are capable of generating maps with uniformity as well as processing data from different platform.
Types of Basemaps:
Maps always communicate
a message. So in order to communicate your message, it is important to
choose the right type of basemap.
Although various types
of basemaps exist, there are generally just several in use today. Each one has
its own benefits and disadvantages when it comes to displaying and conveying
information.
Here is a table that
describes the types of basemaps and a bit of background on what situations you
would use them.
|
Basemap |
Description |
|
|
Orthophoto |
Orthophoto basemaps show ground features with
detail from a top-down perspective. They are usually created by satellite
imagery, but can also be created with aerial or drone photography. Its major
advantage is that you can see the features of Earth and even measure
distances with anything from buildings to streets. Ex. Google Satellite
Imagery |
|
|
Topographic |
Topography is the underlying foundation of a
landscape and can refer to mountains, valleys, and rivers on the surface. A
topographic basemap generally includes elevation in the form of contours. But
it can also incorporate natural and artificial features such as
administrative boundaries, hydrography, parks, urban areas, and
transportation. Ex. USGS Topographic Basemaps |
|
|
Satellite |
Satellite imagery provides users with an
aerial view of a location captured from space. This is a useful type of
basemap if you want to see any features with an aerial view. Because
satellites orbit in a circular path with repetitive acquisitions, it’s capable
of capturing imagery with up-to-date information. Ex. Sentinel-2 Views |
|
|
Elevation |
A digital elevation model, also known as a
DEM, is a digital representation of the elevation surface of the Earth.
Elevation is the vertical distance between the ground surface and an
ellipsoid model or geoid. This is useful for depicting any type of
construction project as elevation can add extra cost. Ex. SRTM Digital
Elevation Model |
|
|
Contours |
Elevation contours are just another way of
showing how elevation changes in geographic locations. These lines show
constant heights of elevation. Lines closer together represent steeper
terrain. Whereas lines spaced further apart show gentle slopes. Ex. Contour
Map |
|