Map Grid of Australia (MGA)

See also SPM or State Permanent Mark

For GDA94 read MGA (my words)

The following is a brochure authored and distributed by the Department of Primary Industries Water and Environment, Information and Land Services Division, Tasmania. 

IMPORTANT INFORMATION FOR USERS OF MAPS IN TASMANIA

A new datum is being used for mapping and spatial information in Australia. This leaflet describes how the change will affect Tasmaps and other products published by the Information and Land Services Division of the Department of Primary Industries Water and Environment, Tasmania (DPIWE)

Background

The new datum, Geocentric Datum of Australia 1994 (GDA94) is being progressively introduced by all government mapping agencies throughout Australia. It replaces the Australian Geodetic Datum 1966 (AGD66).

The primary reasons for making the change to GDA94 are:

• It is compatible with the datum used by global navigation systems, such as the WGS84 datum used by the satellite-based Global Positioning System (GPS).

• It is compatible with national mapping activities, such as hydrographic charting, which are already based on WGS84.

It will provide a single standard for the storage, management, analysis, and display of spatial information throughout Australia.

The Information and Land Services Division of DPIWE has started publishing maps on GDA94. All new 1:25,000, and series maps published after 31 March 2003 will be based .on GDA94.

How does GDA94 differ from AGD66?

The GDA94 datum defines a mathematical surface that best fits the shape of the earth as a whole with its origin at the earth's centre of mass, hence the term "geocentric".

The AGD66 datum defines a shape that suits the Australian region, with an origin that does not coincide with the centre of the earth, a non-geocentric datum.

Because the datums have different origin points, GDA94 and AGD66 coordinates differ by approximately 200 metres in Tasmania.

How does the change to GDA94 affect maps?

The change will show as a shift in the position of the grid lines and a corresponding change in the coordinates of map features. The amount of this shift will vary according to the scale of the map.

Map Scale Shift (mm)

1:25,000 8

1:100,000 2

1:250,000 0.8

GDA

The map borders will also shift, so they will not align with adjacent AGD66 maps. In the case of 1:25,000 and 1:100,000 series maps in Tasmania, the area covered by new GDA94 maps will be extended so that they abut adjacent AGD66 maps.

How do I know if a map is based on GDA94?

All maps published by DPIWE state the datum in the border information. GDA94 maps will be readily identifiable because they will display the GDA logo and they will contain conversion notes which describe how to convert coordinates from one datum to the other. The cover of the new 1:25,000 series maps will differ from their A13D predecessors.

This map is based on the Geocentric Datum of Australia 1994 (GDA94)which has superseded the Australian Geodetic Datum 1966 (AGD66). The datum for heights remains the Australian Height Datum (Tasmania).

HORIZONTAL DATUM CONVERSIONS

AGD66 to GDA94

Latitude
Decrease by 5.4 seconds
Longitude
Increase by 4.8 seconds
Easting
Increase by 112 metres
Northing
Increase by 183 metres

GDA94 to AGD66

Latitude
Increase by 5.4 seconds
Longitude
Decrease by 4.8 seconds
Easting
Decrease by 112 metres
Northing
Decrease by 183 metres

The accuracy of the coordinates obtained using these conversion values will be consistent with the stated accuracy of this map.

For most practical purposes GDA94 coordinates are compatible with satellite derived coordinates based on the World Geodetic System 1984 (WGS84).

GPS users please note If your receiver does not have a GDA94 datum option, use WGS84

GDA

How will the change to GDA94 affect navigation?

The change will not be noticeable if you are using basic navigation techniques. These include identifying your position by referring to map features, and using a magnetic compass to determine your position or follow a route.

If you are using a GPS receiver in conjunction with a map, note carefully which datum the map is based on and set it in the receiver. If the map is based on GDA94 you will need to set the receiver datum to WGS84. This is because currently most GIPS receivers do not recognise GDA94. For map reading and navigation purposes, WGS84 can be regarded as identical to GDA94.

If you are plotting or quoting grid coordinates or grid references, it is now important to note the datum. They then can be accurately positioned on maps or entered into a GPS, based on either datum.

Will the change affect contours and heights?

No. The datum used for heights is not being changed. It remains the Australian Height Datum (Tasmania) which is based on mean sea level.

Market Appraisal (Appraisal of Value): An opinion by a real estate agent who is not a registered valuer of the potential selling price. 

Market Value: The most likely price that will be given by a well informed, willing but not anxious purchaser for a property owned by a well informed, willing but not anxious vendor. This is a paraphrase of a famous valuation court case “Spencer vs the Commonwealth” 

Marketing Fees: Money invested by the seller that goes directly towards the cost of advertising and promoting the property. 

Marketing Programme: A promotional package put together to give a home exposure to the market. It may include newspaper advertising, open homes, brochures, window displays, Internet advertisements, and a wide range of promotional tools available to estate agents. 

Strata Plan Measurements:

Strata Plan Measurements are structured differently to those of 'normal' Survey Plans.

The whole concept of the Strata Plan Boundary definition is that it is, wherever possible, defined by physical features or offsets to these features rather than Bearings and Distances.

This is in fact the concept behind boundary Definition where Monuments have precedence over measurement. See Survey Methodology.

Measurement that may be shown on a Strata Plan are shown only to assist the interpretation of the plan in terms of 'which bit of occupation is being referred to here'

For this reason, measurements shown are to a lower degree of accuracy than normal Survey Plans, as is the resultant areas of lots etc.

That is, the precise horizontal and vertical boundaries in a strata plan are defined verbally along physical structures.

The legislation at section 5(1)(f) also requires that "a strata plan must show the approximate area of each lot"

If a difference in measurement is encountered, say by an amending strata survey, the important issue to remember is that the physical structure has not changed, only the measurements shown to assist in its description.

Minimum Area: usually relates to the minimum lot size allowed in a particular zone in a Planning Scheme.

SIMPLY:

A term used to describe the smallest lot size allowable.

HOW WE ASSIST:

We can asses Planning Schemes to determine what lot size is applicable to your area.

Contact us for advice in relation to these matters. 

Minor: A person under the age of 18. In Tasmania, a person under 18 cannot be registered as the owner of real estate. 

Misrepresentation: Something said or done which creates a false or wrong impression, usually in the context of understanding in a contract. If the misrepresentation is fraudulent (that is, it was intended to mislead) the wronged party can take action for damages or it may involve criminal proceedings. If misrepresentation was innocent (that is, a genuine mistake) the wronged party can usually choose to continue with the contract or void it. 

Mortgage means a financial arrangement where a land owner borrows money and hands over his or her title as security to a lending authority. The title is then held by the lending authority (the mortgagee) until the principal amount and any interest has been paid off by the borrower (the mortgagor).

A Torrens Title (Real Property land) mortgage document is registered on the borrower’s title and may be discharged upon the payment of the loan.

A general law ('Old System’ land) mortgage transfers the legal estate and the mortgaged property is actually conveyed from the borrower (mortgagor) to the lender ( mortgagee). The mortgage is discharged by reconveyance, where the legal estate is transferred back to the borrower upon the payment of the loan.

SIMPLY:

Real Property land has the mortgage registered on the ‘one single document’, the title. Old System land actually transfers the ownership of the land to the lender, to be later re-transferred after payment of the debt.

HOW WE ASSIST:

We can advise the mortgage situation with your title and it’s implications on transactions that you may be considering. 

Mortgage Guarantee Insurance: An insurance agreement protecting the lender against loss. Mortgage insurance means that the lender, a Building Society for example, can confidently make advances for homes where the borrower has a lower equity than the accepted margin. The lenders are protected against loss on the loan should the borrower default on the repayments or other covenants of the mortgage. The mortgage insurer will reimburse the lender for the total amount of the loss, which may also include, costs of selling the property, essential repairs, and maintenance, unpaid rates and so on. Where a person defaults under the mortgage, and the mortgage insurer pays the lost amount to the lender, the borrower will remain liable for the loss. 

Mortgagee :The person to whom the property is mortgaged; the lender of the mortgaged debt. 

Mortgagor: The person who mortgages the property as security for the mortgage debt; the borrower. 

Multiple Listing: A system where an owner gives one agent an exclusive agency under which it is his or her obligation to invite other agents to assist in the sale of the property for a share of commission.