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Nova Scotia's
Geographic Information
Standards
Chapter 3
Spatial Reference System
3.0 Introduction
A spatial reference system is a coordinate system based upon survey measurements used to
define the relative and/or absolute location of features. This system includes a geocentric
ellipsoid of revolution, a map projection system, a sheet layout and a sheet numbering system.
Over time this chapter will contain standards material related to all aspects of spatial referencing
systems, everything from basic map sheet naming to defining the vertical and horizontal datums
for provincial base mapping.
3.1 Topic: Map Sheet Referencing - Provincial Map Series (1:10 000 and larger)
3.1.1 Purpose: This standard will allow the consumer to better reference the 1:10 000, 1:5
000, 1:2 000, and 1:1 000 products they wish to obtain.
3.1.2 Standard: Adopt the NSGC imperial and metric map sheet identification numbering
system, as an interim standard numbering system, for the existing 1:10 000 scale and larger,
map series.
3.1.3 Description:
There are 3 provincial map series in place today. Each having their own unique reference
system. They are the Metric; Imperial; and Orthophoto series. Below is a brief description of
how each of these map series are referenced.
3.1.3.1 Metric Map Sheet Referencing System
Standard metric map sheets vary in scale and of course level of detail. The selection of a map
sheet referencing system was predicated on the need to have the system flexible for all metric
scales. Table 3.1 highlights popular metric map scales. While the metric map sheet referencing
system is not intended to apply to map products produced by the Federal Government, this
system could well be applied to the 1:50 000 and 1:250 000 map series.
How does the metric map sheet referencing system work?
The numbering standard adopted for these maps is based on a 13 digit code. This code contains
the map sheet scale and spatial details related to that sheet. Table 3.2 provides examples of how
the metric code is adopted for a variety of scales.
Table 3.1
Popular Metric Map Scales
|
Category of Scale |
Map Scale |
Step in Decimal
Degree of Latitude |
Step in Decimal
Degree of Longitude |
|
Very Small Scale |
1:1 000 000 |
4.0000 |
6.000 |
|
1:500 000 |
2.0000 |
4.000 |
|
1:250 000 |
1.0000 |
2.000 |
|
1:125 000 |
0.5000 |
1.000 |
|
Small Scale |
1:50 000 |
0.2500 |
0.500 |
|
1:25 000 |
0.1250 |
0.125 |
|
Medium Scale |
1:20 000 |
0.1000 |
0.200 |
|
1:10 000 |
0.0500 |
0.100 |
|
Large Scale |
1:5 000 |
0.0250 |
0.050 |
|
1:2 000 |
0.0100 |
0.020 |
|
1:1 000 |
0.0050 |
0.010 |
|
Engineering Scale |
1:500 |
0.0025 |
0.005 |
|
1:200 |
0.0010 |
0.002 |
|
1:100 |
0.0005 |
0.001 |
Table 3.2
Examples of Map Scale and Referencing System
|
Scale |
Referencing System |
|
1:10 000 |
1045700061300 |
|
1:5 000 |
0545675061300 |
|
1:2 000 |
0245640061300 |
Each map sheet reference starts with the first two digits representing the map scale. The next 6
digits refer to the latitude of the southeast corner of the map sheet. The last 5 digits refer to the
longitude of the same southeast corner(1). Please refer to Figures 3.1 and 3.2 for more details on
the referencing system.
Figure 3.1
Example of referencing system breakdown
Figure 3.2
Hierarchy of Metric Map Series
3.1.3.2 Imperial Map Sheet Referencing System
While the province has been striving towards the full use of the Metric Map Referencing System,
there are those products which have an Imperial Map Sheet Referencing System. As with metric
map sheets, imperial map sheets have a variety of scales and levels of detail. (2)
How does the imperial system work?
The constructs of the Imperial Map Referencing System is based upon a hierarchical system.
Each imperial series fits into its "parent" system. Figure 3.3 provides an example of how the
system is structured.
Its naming conventions however are not completely bases upon a hierarchical system. All
provincial imperial series can be referenced back to the older 1:24 000 scale imperial system. In
the case of the province's 1:4 800, 1:2 400, and 1:1 200 only the 1:2 400 and 1:1 200 series are
hierarchical in nature (see Figure 3.4 for examples).
Figure 3.3
Imperial Referencing System 1:4 800 to 1:1 200
Figure 3.4
Examples of Imperial Map Referencing System Breakdown (3)
3.1.3.3 Orthophoto Map Sheet Referencing System
The Orthophoto Map Series covers the entire Province of Nova Scotia. It was completed in the
early to mid 1970's at a scale of 1:10 000 (based on the NAD27 datum). This series must not be
confused with the 1:10 000 metric map series (which is based upon ATS77 datum).
How does the orthophoto series work?
The Orthophoto series has often been referred to as an "Imperial Map Series". Such a reference
can be misleading. In the early to mid 1970's the provincial orthophoto map series was based on
the imperial map sheet layout. In the late 1970's, however, the series was based upon the metric
mapping system. As Figure 3.5 (see next page) depicts approximately two-thirds of the province
has orthophoto map coverage in the imperial system, while one-third is based upon the metric
system.
Figure 3.6 highlights an example of the Imperial - Orthophoto Map sheet referencing system, a
metric sheet reference would mirror the 13 digit system described on page 3-3. The diagram in
Figure 3.7 depicts the reference system used for the imperial orthophoto series as it relates to a
1:50 000 NTS map sheet, based upon the 2.5 minute by 5 minute window. The metric
orthophoto series would, of course, be based upon the 3 minute by 6 minute window
Figure 3.5
Figure 3.6
Example of Orthophoto Referencing System in the Imperial System
Figure 3.7
Imperial - Orthophoto Map Series Reference System Based on a 1:50 000 Series Map
3.2 Topic: Map Sheet Referencing - Federal Map Series
3.2.1 Purpose: This standard will allow the consumer to better appreciate and reference the
federal mapping products.
3.2.2 Standard: Adopt the National Topographic System (NTS) map sheet names and
numbering system for scales of 1:50 000 and 1:250 000
3.2.3 Description:
3.2.3.1 NTS Map Sheet Naming Convention and Numbering System
The NTS map sheets operate on a hierarchical naming convention. Figure 3.8 provides an
example of this convention and Figure 3.9 indicates graphically how NTS series maps interrelate
to one another.
Figure 3.8
Example of NTS Naming Convention
Figure 3.9
Interrelationship of NTS map scales
Figures 3.10 and 3.11 highlight those areas of the province covered by 1:50 000 and 1:250 000
scale digital mapping. While the conventional map series for these scales also use the same
indexing systems, the person requesting conventional mapping should be alerted to the fact that
some of the maps depicted on these indexes do not exist in hard copy. For example, the 1:50 00
maps 20P15 and 20P10 are two separate digital map. If someone was to attempt to locate the
20P10 sheet in hard copy NTS format, it would not exist. Its content is included on the 20P15
hard copy product.
Figure 3.10
Figure 3.11
Endnotes:
1. Why the Southeast Corner? In the early 1970's it was decided that map referencing was to be
based on the maps minimum X and Y values. Because the minimum X and Y's for a map sheet
are the lower right (S.E.) corner, all map sheet were referenced this way.
2. Imperial series maps show grid measurements and contours in feet rather than metres.
3. Imperial Map Series will begin with either 4 or 5 to signify the two possible imperial zones
found in the province.
 Chapter Three Table of Contents
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